Technical Fiat Coupe 20v Turbo won't idle!

[HomerJ20]

Hey guys,

So about a week ago I was driving home and my 20v Turbo coupe starts sputtering. I slowed down for a speed hump and the car nearly stalled. I managed to get the car home and while going into my driveway the car stalled completely. I sat in the car for a bit, started it once again, it went up to about 2000 rpm then stalled completely. I can't drive the car because it doesn't go past 2000 rpm! But the strange thing is, when I sprayed carb cleaner into my air intake box the car starts and idles fine then shuts off again. I did a bit of research and one source said it could've been my MAF sensor went bad. I replaced it today (after waiting a week to have it shipped from the UK to the Caribbean) and the car still wouldn't start! What else could be the issue here? I also checked my injectors and they were all fine. My injector light too comes on and stays on for a bit then goes out. Anyone else experienced this issue? Thanks in advance.

 

[Neverth]

So idles fine when there is something to burn?
Fuel pressure?

 

[HomerJ20]

Ok so update on this...I got the car to start. Thing is, I had to unplug the MAF for it to start, but when I plugged it back in the car stalls. The car also drives, but on cold start it runs a bit rough until the engine is warm. The injector light on the dashboard remains on as well. Not to mention I purchased a brand new MAF and it still isn't working proper! Any work around to this issue?

 

[Neverth]

Original Bosch MAF? If you bought something else, it will most likely not work as atleast N/A 20v engines reject those. And even Bosch one might be broken (I had to warrany one as it was DOA).

Unplugging the MAF just makes the engine to run in open loop ignoring some sensors, erratic idle is normal as it has no idea how much air is going in, only a good guess. Once warm the lambda can compensate a little and the closed loop map is for warm engine.

It seems like sensor issue.

Did you read the codes for the injector light?
You can also read the measured air mass from the MAF while engine is running to see if it is working (I used this to measure fuel usage on N/A 20v until I switched to measurement from injection time).
Read other sensors too to see if something does not look right (intake air temperature and manifold pressure are two important ones).

It could also be something simple like corroded ground connection on chassis/engine.

 

[HomerJ20]

I haven't done any diagnostic tests on the MAF. To be honest, I dunno where to begin. The MAF I purchased was not an original Bosch sensor. With the old sensor, I would spray a lil carb cleaner into the airbox and the car would idle fine until the fumes die off. I even blew air into the sensor with my mouth while the car was idling and the car shut off. So I assumed the MAF was bad and purchased a new one. Now i've purchased it, same crap all over again. Please note I am thousands of miles away from the UK, so getting my coupe under proper diagnostics isn't gonna happen. Could it also be a ground wire problem? If so where could I begin to look to remedy this issue? These coupe's I tell you are a pain in the rear! But god awfully lovely when running properly.

 

[Neverth]

Laptop+Multiecuscan+KKL cable with 3-pin adapter is enough for diagnostics.
Unfortunately the 20VT is not supported by the free version.

If it idles with MAF disconnected, it is something to do with air input.
And MAF is analog so it could be disturbed by bad connections.
I'd still think it should inject some fuel when starting even with bad MAF as ECU should see that the throttle is not closed and there is some vacuum in the manifold.

Check the connection between the block and chassis with voltmeter when starting (resistance check might show OK, but under load the connection may fail). Near zero is ideal and I'd say over 1V is bad.
Do the same with ECU case and the engine block (I dont remember if the case is grounded, but it sounds reasonable, some have attached additional ground wires to the ECU mounting bolts), this should show millivolts at best.

On the MAF connector, pin 1 is ground, pin 2 is power (sensor+ from ECU, might be low voltage, I'd need to measure it myself), pin 3 is power (heater+, should be ~battery voltage) and pin 4 is signal to the ECU.

 

[sumplug]

This is the idle control valve, that is partially blocked. Very common on Coupes. Simply take it off, clean it with WD40, and refit. Idle should be fine then.

 

[Neverth]

Does it cause the revlimit to shift to 2000rpm?
Isn't 20vt cable throttle so it still should open and rev past it even if the ICV is stuck.

 

[sumplug]

Ah, if no revs, we are talking maf sensor possibly. With no signal, the ECU will set the air to the middle, so on a cold engine, it will run rough until warmed up. The wiring does take a battering, going to the Maf.
A continuity test is needed, between ECU and Maf. Either faulty Maf, or broken wire.
Cleaning the ICV, should be done anyway. They do clog up.

 

[h2ypr]

Did you get this sorted?

 

[elberto]

This is the idle control valve, that is partially blocked. Very common on Coupes. Simply take it off, clean it with WD40, and refit. Idle should be fine then.

Pay attention idle control valve (black box on top of mainfold) could be disassembled.
I got changing several valves (all second hand) due I have been cleaning it with WD40 and/or with specific spray, unsuccessfully.....
At the end my mechanic discovered it can be disassembled and deeply cleaned.