MORGAN 4/4: The Zetec Bad Idle Guide

The Zetec is a pretty reliable engine and can last well in excess of 150,000 miles. But if there is one thing that crops up time and time again it is a poor idle. It can be so bad it can stall the car or cause the revs to hang at a bad moment for that. The cars didn't do this during the warranty period so it is not something you need tolerate now. What makes it hard to diagnose is that there are so many things that can affect the idle. Some are very common and some rare. I will try to list those I have heard of and rely on the 4/4 owners to report more.

Bear in mind that all 16 valve engines tend to have a rougher idle than their 8 valve brethren. Also the ECU on the Morgan Zetec prioritizes low emissions over good performance so even on a perfect car, there will be some unevenness of idle as the ECU searches for the very lowest emissions. When it occasionally goes too far, it must  increase the revs to compensate.

Although the list here is large and growing, do not assume the Zetec engine is fault-ridden.

Idle Symptoms and Possible Causes/Fixes
Poor idle when warm Vacuum Leak
Crankcase Breather Valve
Plenum Leaks
Pulse Air Injection 
Pulse Air Injection Solenoid
Poor idle when cold Vacuum Leak
Wrong Oil
High hanging rev (normally when cold) Throttle Body Resonance
Poor idle at all times Vacuum Leak
HT Leads
Spark Plugs
Rubber T Piece
Idle Speed Control Valve
Auxiliary Drive Belt pulleys
EGR Valve
Lambda Sensor
Poor idle at some times Vacuum Leak
EGPD valve
HT Leads
Spark Plugs
Inlet Air Temperature Sensor
EGR Solenoid 
Heat Soak 
Throttle Body Gasket
Throttle Body Position Sensor
Bad idle and stalling when warm Loose Eprom

HT Leads

These commonly break down, often in only a few thousand miles. They show as a slight stutter when idling or a misfire at high load. Best diagnostic is to swap for a known good set.

The Zetec produces a very powerful (and reliable) wasted spark from the capacitor discharge coil. But due to the large plug gap Ford specifies, the current must be very strong to create a good spark at the plugs. This puts a lot of stress on the HT leads and they often fail. Don't replace them with a cheap quality. Ford or Splitfires are suggested. Bosch, Halfords are not.

Be careful when removing leads. always rotate the lead to break the suction and stickiness before pulling the boot firmly. Never pull the lead. Always change plugs and leads as a set as a problem in one can damage the other

Spark Plugs

Not normally a problem if you use good plugs. Use NGK,  Ford Motorcraft. BEWARE. If you use Champion plugs, you have found your problem. You can also try gapping them a little less as suggested above. (1.1mm rather than the recommended 1.3). HT leads last longer and the engine seems smoother at idle. Always change plugs and leads as a set as a problem in one can damage the other

Rubber T Piece

Hiding underneath your coil is the most vulnerable part of the Zetec and few seem to know its there. It is a 5cm rubber T-piece that connects the engine block to the EGR valve and the Pulse air system. Due to the movement of these pieces it often splits and lets out vacuum, resulting in a bad idle and or stalling. Many Agents know  about this item and it is one of Ford's best selling spares for the Zetec. At £6, it is cheap. Be careful that you are not given a tale about sticky valves or some such and simply switch that piece of rubber. However, IF your plenum is in place it can take longer.

To remove, stick your hand under the coil (towards the rear about 5cm below the coil base). Feel for the rubber bit and pull firmly. It takes about 20 seconds to swap it.

On my coil, the t- piece connects the thick silver tube on the lower left to the thin tube to the right of the coil, and the third way goes to the engine block. It just pulls off

It is part 8A on the diagram.

EGPD Valve

The big villain of a bad Zetec idle is the Exhaust Gas Pressure Differential Valve (EGPD). It resides in in a silver box that has 2 rubber hoses and a 3 wire multiplug to it. Check the hoses are not perished and the plug is connected. Its about £45 to replace but has worked many cures on many Zetecs cars. No easy test for this one other than swapping it out. Try cleaning out the pipe ways with throttle body cleaner.

When it malfunctions, it switches the EGR valve in and out when it shouldn't, resulting in a lower crankcase vacuum

The EGPD Valve is the silver box on the right. Also check the rubber vacuum lines running to it for cracks or splits.

The Crankcase Breather Valve (Positive Pressure Valve)

This is an inexpensive item. £8 for a small metal valve. Yet it can be the cause a very lousy idle. It is designed to allow excess crankcase pressure to escape. When partially blocked, it results in a bad idle. It will stall the engine when completely blocked.

Ford says that it should be changed at 30,000 mile intervals but then they forget to mention that in their service guides and Haynes forgets it entirely. I am told it is very difficult to change. Symptoms of blockage are a decent idle when cold, which gets worse as the engine warms and then leads to complete stalling at working temps. The engine seems to pulse and hunt with a one second frequency between 1500 and 700 rpm

The arrow points to the rubber tube running to it. To change it, remove the rubber T piece under the coil. Reach under the thermostat housing and you will find a small T3 (sometimes T4) bolt holding the metal pipe on. Remove this. Now reach your hand in under the pulse air piping and give the rubber tube a good pull (Pliers help) and the valve should pull out. Use some sealant as you replace it, as the rubber grommet it sits on can be very brittle and hard.

Vacuum Leaks

There are a great deal of thin rubber vacuum lines on the Zetec. If any are leaking or damaged, the vacuum will drop and the idle will be terrible. Most run from the two outputs from the back of the throttle body (top center of picture below). Remove these and blank them off. If the idle improves you have a leak downstream of them, replace one to determine which and follow the tubing down to find the leak. I have an alternative method. Buy a spray can of ether. It is sold as QuickStart or under other names to help starting your car. With the engine running, use short bursts on different areas of the engine..(but not the air intake). If the idle changes, you have found your vacuum leak.

There are many vacuum lines around the Zetec engine. The plenum chambers can also chafe vacuum lines. Alternatively, you can also use a vacuum gauge and test. You should have a nice steady 17-20 psi vacuum at idle. Cure the leaks, cure your idle.

Look here under plenum leaks.

Idle Speed Control valve

There is an idle speed control valve. This allows small variations in idle speed to be smoothed out. It works by varying the amount of air allowed into the engine via an auxiliary air passage in the throttle body housing. It is controlled by the ECU. This valve is open to the inlet manifold and therefore it gets dirty over time. One can remove it and carefully clean it by soaking it in throttle body cleaner. A replacement valve is £34.

The valve can be removed with the plenum is off, but is awkwardly placed and you will need the right socket extension. Stick your hand in under the TB and intake manifold. There are 2 bolts holding it on.

Its situated under the black inlet manifold and you will not be able to see it so you must remove it by feel. DO NOT drop the bolts either and MAKE SURE sure the gasket is intact when you replace it. New units come with a new gasket.

Throttle Position Sensor (aka throttle pot)

This sensor provides the ECU with data regarding the position of the throttle butterfly plate (i.e. how far open or closed). It consists of a potentiometer mounted on the throttle shaft. It is easy to remove from the throttle body via the two screws, don't forget to remove the wiring's connector. To replace just line it up and stick it on. It is spring loaded and so it returns to the correct place.

To test, use a multimeter and while watching the resistance, gently rotate the inner spindle (don't force it), you should get a nice gentle sweep of resistance. Any spike or anomaly's and its dead. Unfortunately the place its most likely to wear is the idle position which is hard to test. You can wash the inside out with WD-40 as a precaution. A new one is £25.

When refitting make sure the rubber seal on the throttle body is intact and flat. There have been problems with this seal distorting and sitting the potentiometer at an angle which forces it to give erroneous readings.


This is the most important sensor. It measures the quantity of air passing into the engine. This information is then fed back to the ECU and the engine compliments the air with a pre-determined amount of fuel taking into account varying ambient conditions. It is clever device consisting of a hot wire that is kept at 200C . When air blows over it,  the wire cools and the ECU fueling, power and air intake to keep the wire at 200C. So the fuel provided is proportional to the air flow. Also when you stop it heats the wire up very hot (300C) for a second or so to burn off any dirt. Unfortunately that dirt can remain on the wire. This insulates the wire and gives false readings. You can prolong the life of your MAF by gentle cleaning with throttle body cleaner using a thin paint brush. Don't spray hard on the wires,  they are very delicate.

When removing the MAF, make sure you don't pull on the wires, but gently hold the plug

There was a big problem with early cars as plug contacts and MAF are alloy and corrode, prejudicing the contact. Ford now makes these using gold contacts. They also have a kit for converting the old connectors to the gold contact one (with lots of soldering). When you reconnect make sure that it really is firmly in and that none of the wires are broken. Its worth disconnecting and replugging this every now and then to ensure the contacts are clean and making contact. A new MAF is £80. A good one makes a huge difference to the performance. Symptoms of a bad MAF are a slightly rough idle and low power.

Lambda O2 Sensor

The lambda provides the ECU with data relating to the quantity of oxygen remaining in the exhaust gas. With this information the ECU can enrichen or lean out the air/fuel mixture to reflect the fuel map parameters. It is also necessary for the correct operation of the catalytic converter.

N.B. The sensor does not operate until it has reached its working temperature.

Lambda sensors last about 80-100k miles before they die. A dead one generally gives all sorts of running problems and lack of power including a bad idle when warm. (Not when cold). You can check the voltage from it properly only with an oscilloscope as it pulses its signal. So either swap it out or go to a garage for testing. Make sure you don't touch the tip of the probe or you will contaminate it.  Later Zetecs have two, one per exhaust.

Throttle Body Resonance

This is another common problem with the 1.8 Zetecs. It is a manufacturers' defect and the subject of a Ford recall;

Model: Focus with 2.0L Zetec-E engine with MTX 75 transmission built from 11.1999 to 07.2000 (build codes XM to YD)
Markets: All
Subject: Intermittent high idle or idle hang up (above 2000 rev/min) with/without moose noise


Should a customer express concern about intermittent high idle or idle hang up between 2000-4000 rev/min with or without a moose noise mainly when coming to a stop, the probable cause is acoustic resonance of the inlet air control (IAC) system. This concern should be rectified by installing a new intake manifold, distributor vacuum hose and crankcase vacuum hose.

Production Action

A revised intake manifold has been installed in production since 08.2000 (build code YE).

Also look HERE

The defective components should have been replaced by your Morgan dealer, claimed against the Company and they will claim from Ford.. However, I have heard that the MMC refuses these claims beyond the warranty period. Ford did not.

It has also been reported that a European Morgan dealer found a cure without, apparently, (from the forum emails) understanding the cause. He fit a metal spacer into the throttle body. This extra  hunk of aluminum apparently dampens the resonance to allow smooth running at idle (but with unknown effect on performance otherwise).

Sadly, some owners have also used restrictor plates to stop full airflow and that too will stop the a very deep cost to performance. The best solution is to fit a new intake manifold, distributor vacuum hose and crankcase vacuum hose made as directed by Ford.

Inlet Air Temperature Sensor

This provides the ECU with a signal indicating the temperature of the incoming ambient air. Confirm that the connections are good and that the sensor is in position. A new one is only £16 so its probably easier to swap it rather than worry about testing. Its situated on the underside of the plenum tubing about 20 cm away from the MAF (where the forward plenum joins). It just unscrews once you've disconnected it.

Throttle Body Gasket

This is plastic and quite brittle when old. It is cheap to replace at £4. If it is leaking then your engine is getting un-metered air into the engine which will alter the idle. Most of these gaskets split the first time the throttle body is removed. However, most people don't realize it is there (black gasket on a black inlet manifold) and therefore it is often inadvertently re-used.

Plenum Leaks

Easy to check. Make sure all the connectors on the plenum tubing are tight and snug. Especially the bolts to the throttle body, Check that the throttle body to plenum join has the O ring in it and is sealing (Easy for O ring to fall out). Any leaks here will let in un-metered air and kill the idle smoothness.

Heat Soak

The Morgan engine bay has good air flow while you are moving but when you stop it gets much less, and the temperature begins to rise rapidly. As the intake draws its air from the engine bay then the hot air its now collecting is less dense. The inlet air temp sender will delay a bit to change the temp reading resulting in an a lumpy idle until it does. Components also get very warm and could heat the inlet air temp sensor to engine temps rather than air temps. It is wise to fit the air temp sensor into a rubber inlet section rather than the metal ram pipe.

EGR Valve

This allows a measured quantity of exhaust gas to be directed back into the inlet manifold. The exhaust gas introduced into the inlet manifold dilutes the incoming mixture and reduces peak gas temperatures thus reducing NOX emissions. The valve is vacuum operated and controlled by the ECU IV module. The EGR system does not operate during conditions of over-run or wide open throttle. The image here is one of a shiny new EGR valve. Note the vacuum hose running from the front of it. You can see the base of the inlet air temp sensor above it.

The EGR valve is controlled by its solenoid and the EGPD valve. If it activates at the wrong time it will decrease performance and hurt idle. It can also physically fail which results in a vacuum leak. Remove the old valve and clean it with throttle body cleaner. Check if its diaphragm is intact. To tell if it is working remove its vacuum line from the other end and suck hard. It should stall out a running engine or make it run very poorly.

In time, the diaphragm will fail. Their cost is £50 and they are easy to fit. Unscrew the nut underneath it and remove the two bolts. No need to move or loosen the pipe running into the bottom.

EGR Solenoid

This uses the vacuum pressure to sense when to open and close the EGR valve by allowing vacuum to it. Often its hoses rot. It is shown here. Replacing it is easy, just pull off the hoses and undo the 2 screws. Don't drop them. Cost is about £32

Pulse Air Injection

This allows fresh air into the exhaust manifold. The purpose  is to further reduce emissions. The system is also ECU controlled. The valves and filter are combined in a single assembly. The system operates only until the HEGO has reached its operating temperature and the ECU is providing closed loop control (typically 20 seconds) and on deceleration (closed throttle).

When it is defective you will hear a loud clacking noise that sounds like valve rattle. There is a foam filter in the black plastic box which can be cleaned. You can take the black plastic box from the pipe work and clean it. But that will probably not help. Fitting a new unit will.

The pulse air injection unit is sold as a single assembly for £200, including the valve box and new tubing. You can do the swap with the exhaust in place. You can see the silver piping and the top of the valve box in the image. .

Pulse Air Injection Solenoid

Uses vacuum and ECU information to turn the pulse air injection system on and off.  Here is an image.

To test, go under the front of the car and remove the vacuum line from the pulse air injection system black box. Connect a vacuum gauge. You should get vacuum only on a cold engine and overrun. If there is any vacuum at idle on a hot engine then the solenoid is broken. Replacement is £31 and just the two screws hold it on. A very rough idle to stalling are the symptoms

Wrong Oil

If you have used too thick a grade of oil (Such as 15W/40) then this could effect the hydraulic valves, causing them to be sluggish until warm which could give a rough cold idle. This is what people think of as the "Sticking Valves Problem" a quick oil change to the correct viscosity oil will fix this. Symptoms are valve rattle noises on start up which go when warm. If you don't cure this the the valves will wear and you'll have a permanent rattle.

Use Mobil 1. The best prevention is to use the correct grade oil. Ford say that you should use a min of 5W winter rated oil (so 10W is bad). If you have put in the wrong oil or don't know what is in there then do an oil change using a synthetic 5W-30 oil, leave this in for a couple of weeks to spread round and dissolve/pick up the gunk and then change again to your main oil Do not forget to change the oil filters whenever you change the oil

Auxiliary drive belt pulleys. Bearing Failure

Very rare but not unknown. If one of your pulley bearings or the water pump bearings are going, this will put a strain on the belt and therefore the engine and this could effect the idle speed. Difficult to diagnose. Check the belt tension and listen to the belt area for strange noises. remove the belt and rotate each pulley by hand. Feel for any tightness of free play. Replacement is the only option.

4/4 Ford 1800cc Zetec ECU: Problem and Fix Explained.
by Philip Young


You would be driving along at 70 + and the engine would suddenly start cutting in and out. Drive along for a few more miles and then the engine would cut out completely. Wait about 2 minutes without doing anything, restart the engine and everything would be fine. Initially this would only happen once in a while but eventually it happened on a regular basis. So I took the car to EFI expert and all the sensors on the engine were checked and all were fine. Of course, the engine never evidenced a problem whilst been checked.

In spite of all this checking,  the final straw was when the engine cut out three times on the way home from Shrewsbury during July 2000. The next evening I sat down and analyzed the thing. I was convinced that there was nothing wrong with the sensors. The only thing that remained to be checked was the ECU, I knew that the previous owner had changed the EPROM on the ECU many times. The next evening I removed the ECU from the car and dismantled it, I removed the EPROM that is only secured with sticky tape and is a push fit on the ECU printed circuit board. The EPROM turned out to be extremely loose.


With a soldering iron (and making sure that you are wearing an earth/ground strap so that you do not damage the ECU PCB components) carefully re-tin all of the EPROM contacts with solder. The PCB is double sided so the contacts on both sides of the PCB have to be tined. Re-assemble the ECU, refit the EPROM and now you will find it is a very tight fit. Secure the EPROM with new sticky tape ( I used tank tape). Fit the ECU back into the car and start the engine. Since I did this, I have had no problems with my engine on this score.