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MG MGF Technical - Engine couldn't idle for approx. 5 mins after bad start: revs kept on dropping to zero + imminent engine cut-out: any idea as regards the cause ?

Encounted the following bizarre phenomenon for the first time with my MGF 1.8i Mpi since its 104K kms history:

Car has been parked all night in my fully closed garage-box (previously however exposed to heavy rain - soakened wet when I parked it yesterday-evening).
Gear is already in neutral, handbrake is still up.
Turned ignition key, waited the usually second until the bzzzz-sound in the back finished, and then fully turned the key to fully ignite the engine.
Engine started but due to a little too slow footwork, the engine cut out again (at least that's what I reckoned). Okay, happened before. Got to be more quickly, I thought.

Pushed the clutch. Waited some 5 secs. and restarted the procedure: this time the engine started but fell out despite normal footwork procedure. So no idling ? This surprised me a little. Hm, what's this ?

Did it over again and same engine cut-out: it seemed like the revs couldn't get grip to idle anymore: revs went up at the moment of ignition, but subsequently immediately dropped to zero-level (followed by a complete engine cut-out).

So I went to "plan B": keep up those revs by continuous play with the accelerator. Okay, not so healthy for the catalyst. And yes, this seemed to remedy somehow the situation, but as soon as I did no longer push the accelerator the revs immediately dropped to zero and engine stalled again.
So I needed in fact three feet: one for each pedal... Solution, use the handbrake to save the foot for the brake-pedal.

So I managed to "drive" to work that way, but even in full motion at a speed of, say, 50 mph, as soon as I risked to push the clutch and no longer the accelerator, or put the gears in neutral, the revs dropped to zero and the engine cut out. So I was forced to use my handbrake to brake, and continuously played with the accelerator to "control" as good as possible the revs above the 900rpm range. Kept me thinking about the cause and how to cure it. Cause: I assume it is caused by some bad/impure fuel particles blocking/impeding the fuel-spray mechanism.

So, after a cut-out or 10, I really got fed up with this "I can't keep up to the 900rpm idle"-niggle, and decided to give the engine a good blast to blow away the bad/impure fuel particles by exposing it to a huge amount of fuel spray: pushed to the 6,800 rpm range(ouch, engine was not warmed up, but hell, I don't want to continue driving like this). And yes: it immediately cured the problem: no cut-out any longer. Once at work a restarted the engine a couple of times to check whether the bizarre engine-cut-out phenomenon re-appeared: all back to normal again.

Anyone experienced this strange phenomenon before ?

Any idea about the cause:
1. engine a bit drowned by fuel due to the first bad start ?
2. bad/impure fuel particles blocking/impeding the fuel-spray mechanism ?
3. combination of 1 & 2 ?
4. something to do with the bad weather circumstances of the previous day (lots of rain fell out of the skies on my MGF)
5. something else (sparking plugs ? battery ?)

And, is this just random or more something like an omen for oncoming engine-trouble (head gasket failure, piston at the brink of breaking up, etc)?

Curious to know your experiences and/or advice.


Blockage in one of the breathers giving false pressure readings? Or electrical shorting?

Not much help - sorry! Wait for Rog, I guess!

Would also suggest that driving to work with handbrake is a little 'risky' - handbrake is not designed for this and the people behind you have no indication that you're slowing.

N837 OGF

Never encountered this one before Luc. Furthermore, my F doesn't require any 'throttle' to start in the morning- even if parked in torrential rain over night.

This is a challenge to my 'old British car owning' skills. And to me, this sounds like a fueling problem. If the car can be started, and once running, the engine runs evenly with no hint of misfire, this to me excludes an electrical fault.

The fact that after a hard run, the problem resolved itself, and the car would restart normally from cold seems to suggest a transient problem- perhaps poor quality dirty fuel blocking the injectors/ reducing the fuel line pressure. Interesting that the problem was mainly at idle- does the MGF injection system have an idle jet?

If the problem recurs, then pop into the local garage and get the car looked at. The reason I say this is because the other problem that may potentially lead to the 'symptoms' you decribe could be a lack of vacuum caused by a failed inlet manifold seal (not uncommon on our early 1.8MPis). This would cause the engine to run lean- not a good idea- and would lead to an inability of the engine to idle due to inadequate fueling. In fact, if your car does require the throttle to be depressed to start the car, then I'd get this looked at sooner rather than later.

Let's see what wisdom Rog has to impart!



Rob Bell

Waow!!!!!!!!!!!! one of the biggest title I ever saw on this BBS!

Re handbrake: you're absolutely right that using a handbrake whilst driving is dangerous:
- you expose yourself to the risk of getting "reared" by cars behind yours, who can't notice when you're braking;
- when it rains you risk to spin off the road

Got no other choices actually. That's why I decided to give the engine a good blast, notwithstanding a rather "cold" engine. I hoped to get rid of the trouble, and it did. So when you ever encounter the engine cut-out trouble: try high rev-range for a short moment.

The reason of using the clutch after a misfire is because I've read it on this BBS: in case of engine misfire, wait a couple of seconds, push the clutch once or twice and then give it a go.

Re idle: I assume this is controlled and "steered" by the ECU. When the MGF is exposed to chilly temps, the rpm will be around approx. 1,200rpm upon engine-ignition, rahter then the usual 900rpm during the first moments.

Re fuel: used the same Esso 95 RON unleaded fuel as always. Didn't confuse with leaded super fuel as I a colleague recently did by mistake on his car :-)

The event still puzzles me. Didn't happen ever since yesterday. Anyway, due to such events, it amazes you how your feet work with the pedals. Sometimes you simply don't realize. Oh yes, when no-one's around, try driving with the legs crossed and you'll be surprised how either of the feet is refined for working with the clutch, brake and/or accelerator. Braking seems to require very sensitive care, or you risk to get involved in a very bumpy ride.

Re long title: oops, thought it had a limited number of characters, quod non ! Oh-oh, text-frame seems a little distorted due to the title...


Page 9 of the Engine Management system section of the workshop manual mentions an idle air control valve, which enables the ECU to control engine idle speed and cold start air flow requirements.

Could this be where the problem is?

The unit is located behind the oil filler cap (the one in the rocker cover).

The reason I know this?

Was talking to an MGF owner last weekend who had intermintent problems with poor idle. After numerous investigations by his MG dealer he sorted the problem out himself by pushing the electric plug back into the unit.



As the engine ran fine at higher revs, and in the end ran ok, I don't think it's blocked injectors, or any of items 1, 2 or 3. Besides, the car has a decent fuel filter. It seems like the temporary failure of one of the engine MEMS sensors, or the ECU failing to interpret what's being sent to it, which could be a result of the heavy rain. Although I'm a culprit too, there's probably nothing worse than putting a car away in a garage when it's soaking wet.

There's no idle jet on the F, the Idle Air Control (stepper) valve provides air to the engine when the throttle is closed, and then the ECU adjusts the advance and retard to hold the idling at a steady speed. The ECU remembers the position of the IAC for a specified idle speed and uses this reference to set the IAC step depending on the temperature of the engine. I'd go for a combination of IAC and ECU, but Testbook should be able to confirm this.

Good Heavens, it almost sounds like I know what I'm talking about!

Regards, Kes.

So Kes, do I need to worry that the phenomemon will reappear or is it likely that it was a mere (mis)fire and forget ?


Hi Luc,

As You have a MPi there could be a problem with the "MAP"-sensor ,Manifold absolute pressure sensor (!)
To check possible blockage in rubber vacuum pipe do as follows: Find ECM unit , "computer box" in engine compartment. Below electric multiplug is a vacuum pipe comming from manifold. Gently release pipe from ECU and blow / suck thruogh pipe to ensure there is no blockage . Also check for damages along full length of pipe. As fuelling is very much dependent on correct info to MAP-sensor any fault here will severly affect engine behavior. Gently reinstall pipe onto (fragile) plastic part on ECU.

Regards , Carl.

Never worked on MGF's, but if equipped with EGR very common for egr valve to kept open by carbon and therefore provide no/poor idle. Racing the engine for periods of time will clear out the carbon and restore sealing ability. Throttle position sensors and idle air control motors could also cause this, but rarely able to fix themselves. TPS easy to check with voltmeter, need graphing ability/frequency reading for IAC is stepper motor type. Check for big vacuum leaks perhaps at PCV or brake booster, if so equiped. Coolant temperature sensor could also be failing and giving incorrect resistance when cold. Best to retrieve any stored codes, if any, in computer memory and start from there or better yet watch the data live if some sort of "scan tool" (as we call them here) is available. good luck.

Sounds as the stepper motor is not functioning as mentioned above, this is located on the air intake plenum, unplug, remove from body and clean the seating /mating face with some fine polish,refit and see if it is cured.
Mike satur

I have seen this on a number of occasions before and every time the cause was WATER. Not the direct spray of water or the dripping water, but the water laden atmosphere allowing excessive dampness to settle inside all sorts of areas, inside the dizzy cap, on the rotor arm, inside the terminal ends of all the electrical connections. In fact everywhere as the engine cools the moisture layer builds up.

The following start, which would have to be at least 3 hours later to a long time hence, (depending on current prevailing conditiuons, temps and ventilation to the garage) now has a problem. There are all sorts of poor electrical connections and so the initial sensor readings to the ems ecu are out of sync. ECU is able to manage controlling the basic function of manifold pressure, engine rpm and throttle position to enable the engine to run, but it is unable to create the coirrect fine tuning control for idle speed and usually light throttle operation.

Running the engine will introduce heat that will start to dry things out and a significant heat input, (6800rpm under load) plus the increased hot airflow generated by the speed of the car, was in this case enough to dry things sufficiently to allow the ems to resume normal control.

You can very simply reproduce this when you wash and engine bay. I don't tempt fate but those who do will have problems washing a cold engine as there is no residual heat to quickly dry things out when the engine doesn't want to restart. (I have gone through a can or two of WD40 when others at work decided to wash their engine bays and engines refuse to restart!!!) In a couple of cases I have seen the residual effect of engine bay washing last for 3 days. In this case the effect was a 1500 rpm minimum idle speed whatever was done to try and cure it. The third day was a warm one and the evening run home was apparantly normal and has been so since. (Rover 214)

So no I don't suggest there is any gremlin waiting around the corner to strike your car and dent your wallet!

Roger Parker


Luc, what a question! I can only say that if it were my car then I'd carry on as usual, treat it as a one-off incident, and mention it to the dealer at the next service. If it happens again then I'd ask the dealer to run Testbook against it, this should determine whether it's the IAC valve or some other component. Testbook can reset the IAC parameters, so I've been told.

Carl, that rings a bell, in the early 90's I had a couple of the first MK2 214s with the K series engine, and they would run fine for some 7-8k miles or so, then start running like a dog. I can't quite remember but it might have been low-speed running. I don't know how I discovered this but I found that if I disconnected the thin plastic pipe that just plugged into the ECU the car ran fine again. The pipe was full of oil and I let it hang loose for a few days to clear before refitting it, and then it was OK for another 8K miles or so. The Rover fix for this was to fit a small fuel trap box into the pipe, just as we have on the F's and other K engines today. This pipe was probably the feed to the MAP sensor in the ECU. The problem with Luc's car apparently cured itself, so these events don't quite fit.

In any event this problem should be identified by Testbook, assuming your dealer has this facility and the capability to use it. Also there's enough good advice in this thread to keep you busy for a while (couldn't answer earlier as my ISP has been yeuk). Good luck!

Regards, Kes.

Kes, your quite correct with description and thoughts for the small plastic pipe, which does pass manifold pressure signals direct to the map sensor in the MEMS 1.9 ECU. VVC engines have a separate map sensor. Since the fitting of the fuel trap things are much better. These traps must always be mounted higher than the manifold connection so that any trapped fluids have the opportunity to drain back to the manifold so a check to see it hasn't detached from it's mounting is another good idea. It is also a very good idea to periodically remove the ends and blow through the pipe to remove any fluids.

Roger Parker

This thread was discussed between 30/05/2000 and 03/06/2000

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