21 Turbo misfire at idle when hot

[21Tpt]

Hi all,

here i am with another issue that has been bugging me for a few weeks and i'm still not 100% sure what's about.

When i start the engine, cold, it runs at first try and very smooth. I can drive it either normally or flat out that everything works as it should.
However, if i stop the engine not enough time to cool down again like first in the morning, it runs at first try but a bit shaky. When i accelerate at first it hesitates but after 2.000 rpm looks normal. If i let it come down to idle, idling is not flat anymore. It varies 100 or 200 rpm up and down. Driving it in traffic is a nightmare because it judders all the time, but if i go flat out it looks normal again
This only happens when the engine is still warm from the previous run.

I've began with the obvious, cleaning inlet manifold, idle valve and still the same. Then i went a bit further and replaced spark plugs with Bosch H3CS, new plug cords from BERU (previous ones were Champion with 6 years old), new rotor, distributor cap and body (that connects to the camshaft). Still same behavior.
Then a bit further again i replaced the water temperature sensor and MAP sensor. Still the same.
I've put WD40 in every plug i could find for every sensor and nothing changed.
Fuel pump is also 5 or 6 years old.
Accelerator potentiometer is practically brand new.

I think i've narrowed it to either one of these that can be malfunctioning:
- fuel injectors (they are 25 years old, maybe they need refurbishing)
- ignition coil or controller (this one i would be surprised because i've replaced the entire thing (coil and controller) 6 years ago. The previous one was there for 19 years )
- fuel pressure limiter (this i'm not so sure, but who knows )

Anyone have any idea of what could be causing the problem?
Can diagnostic computers like XR25 ou Can Clip check each injector, check for ignition coil issues, variation in fuel pressure?

Thank you in advance for any help

 

[Adey]

im not to sure on the cars tbh but i was going to say is there any diag equipment that can be plugged in to read the ecu or data log it to see whats going on @DaveL485

 

[DaveL485]

2wd Phase one right? I've never had a wavy idle on a Phase 1 that wasn't to do with the idle control valve being old, dirty, gummed up or similar. Dizzyless cars are a different story but phase ones have historically always been the IACV (Idle Air Control Valve).

The other problem you describe is an odd one. Several people I know have had it/do have it, My Quadra did it occasionally too, but again this resolved when I changed the ECU...so that would be my next step, change the ECU out for one from a car that doesn't do it.

The XR25 can't check fuel pressure there is no sensor for it, it can show injector ms, sensor readings and basic other stuff but not much more... it was advanced in its day but by modern standards it's a dinosaur lol. Clip ive never tried but I doubt it I would assume thats an OBD plug. An XRD unit will show these readings too or you can put your trip computer into startup mode to get bare readings for fuel delivery, speed and fuel tank level.

 

[21Tpt]

I forgot to tell that is a 1989 late Phase 1.

Since i own the car (11 years), sometimes it would have erratic idling, but usually an inlet manifold clean up would work fine.
However when driving at around 50 mph it has always been a bit shaky. At the time i got it checked for errors and it was complaining about the accelerator potentiometer. I eventually bought a brand new but the problem never disappeared.

The odd thing is that now when starting cold is fine. When starting warm is terrible. It's like some sensor got messed up with the heat. It has never been like this before.

I once swapped the ECU with other Phase 1 but i didn't noticed any difference about the judder at 50 mph.
Does a Phase 2 ECU from 1989/90 work in a Phase 1 from 1989?

I once went to a Renault dealer and they used the Clip device with a cable adapter and it worked. But they just checked for faults and nothing else. I don't know what other options the software had for these older models.

 

[scottyboy1]

Hi , have you checked the TPS sensor , this caused lots of similar issues with my 21. Very slight adjustments make a big difference and are a pain to get set right.

 

[21Tpt]

Hi , have you checked the TPS sensor , this caused lots of similar issues with my 21. Very slight adjustments make a big difference and are a pain to get set right.

Actually that is one of the things i should have checked because it was set in a position where the injection issue light wouldn't come on and i know the value should be set to around 10 at idle.

Before you adjusted yours what value did it had at idle?

 

[DaveL485]

Does a Phase 2 ECU from 1989/90 work in a Phase 1 from 1989?

Yes any ECU from a distributor car will work on any other distributor car (here in the UK anyway).

The temperature related issue is very strange, like heat soak is causing an issue. As I said though mine has completely stopped doing it after the ECU change which led me to think its ECU related. At the end of the day your engine runs on a combination of fuel, spark and compression. The compression is mechanical and wont change. The fuel or spark must be what causes the issue- either incorrect spark timing or weak spark, or a fuel delivery issue.
Maybe try unplugging the knock sensor and see if its messing with the timing? Fuel pressure I can't see being heat related the regs are bulletproof. Injector duration wrong due to a faulty sensor possibly? Without one here to diagnose it's all guesswork on my part!

 

[Red21]

A area of investigation people over look are leaks on the intake system after the throttle valve especialy slight/small leaks
With the engine warm and at idle spray some WD40 around the inlet manifold gaskets in turn, if there is a air leak the engine note will change, also check vaccume pipes for splits, manifold nuts & bolts etc.
A large leakage will generaly be accompanied by slightly higher & rough idle.
A small leak will create hesitation, eratic idle & unpredicable misfire.

Then there is cam belt timing, flywheel pickup, damage to the flywheel target (more common than you think)
One question to ask yourself what work if any was done to the vehicle prior to this problem.

 

[Andyquadra]

If the TPS/throttle potentiometer has been changed, it will need to be set up, both at closed and fully open. Also, you say you changed the water temp sensor, just checking which one, the one in the thermostat housing on the turbo side or the one in the head on the inlet side?

 

[DaveL485]

...as the one on the thermostat side, even though it looks the same as a non-turbo one, has a totally different calibration!

 

[Andyquadra]

...as the one on the thermostat side, even though it looks the same as a non-turbo one, has a totally different calibration!

Just checking. might have changed the wrong one, and as you have said, might have changed the right one with the wrong type

 

[Rob]

I forgot to tell that is a 1989 late Phase 1.

Since i own the car (11 years), sometimes it would have erratic idling, but usually an inlet manifold clean up would work fine.
However when driving at around 50 mph it has always been a bit shaky. At the time i got it checked for errors and it was complaining about the accelerator potentiometer. I eventually bought a brand new but the problem never disappeared.

The odd thing is that now when starting cold is fine. When starting warm is terrible. It's like some sensor got messed up with the heat. It has never been like this before.

I once swapped the ECU with other Phase 1 but i didn't noticed any difference about the judder at 50 mph.
Does a Phase 2 ECU from 1989/90 work in a Phase 1 from 1989?

I once went to a Renault dealer and they used the Clip device with a cable adapter and it worked. But they just checked for faults and nothing else. I don't know what other options the software had for these older models.

I have similar problem tryed same things it's been better as it's colder now tho renault a aye who'd ave em