3200 still cutting out & occasionally unsteady idle

[ledlights]

Hi All,

My long-standing cutting out problem is back - any ideas gratefully received.

I've tried to think through when this all started, so I'll first list the problems and then I'll give the car's problem history.

The problems are:

1. If you drive the car at anything above 1600 rpm and put your foot on the clutch (without keeping the throttle depressed) the engine dies. This is a real pain coming up to roundabouts and junctions.

2. When cold, the engine starts fine. When warm, you have to give it some throttle or it starts then dies immediately.

3. When warm, if you blip the throttle the engine will idle unsteadily for a while afterward (if it doesn't stall).

4. The car will "surge" at 70-80mph as if you are accelerating and decelerating at a frequency of about 0.5-1Hz or so.

5. The car has no "check engine" lights or error codes.

It all started about 3 years ago after I had the plenum chamber plate come loose, resulting in a high idle speed. My specialist repaired this with the original gasket and some instant gasket repair and the screws were thread-locked in. Almost immediately afterward, the TB became faulty so I replaced it with a contact-less one from one of the guys on here. I think the plenum repair and the TB replacement were so close together that you couldn't differentiate when the stalling started.

I've had the plenum off a number of times to check for air leaks, I originally found a split in an o-ring but the problem remains after changing them all. I've checked the plenum plate gasket by pouring a small amount of fuel into the chamber when I'd removed in off the car, but it seems that it's gas tight so I don't think that can be the problem. I've changed the lambda sensors with Bosch replacements and the anti-knock sensors as a precaution and I've also changed the ECU and injection relays. The one senor I can't change is the crank sensor because some helpful soul has rounded out the allen screws but I would expect the crank senor to either fail completely or for it to cause sporadic stalling before springing back to life - as this is what I've seen them do before.

One other thing is that the new TB is quite noisy before and after the engine is running. It "sings" for perhaps 30 seconds after you shut the engine off.

Any other ideas chaps?

 

[allandwf]

Still sounds like a leak somewhere, intake manifold? Agree with crank sensor, any I've come across either fail completely or break down when hot cutting engine but recover when cold.

 

[ledlights]

Yes, I agree but I had the intake off this morning and can't find any leaks. All the pipes are in good condition, the o-rings and plenum plate are the obvious candidates but I can't any leak path.....

Another thought, does the air temperature sensor throw a code if it's faulty? If not, an incorrect or absent temperature reading could cause the car to run lean....

 

[2b1ask1]

Not a Maserati but I chased a similar problem on my sons Saxo for nearly a year and eventually it turned out to be an intermittent fault on the fuel pump; had replaced coil, leads, plugs, throttle body, mass air metre, idle stepper motor valve, choke sensor, fuel filter, had an auto electrician looking at it several times, crank sensor, imobiliser, run diagnostics and more to boot....

Sold it at auction soon after fixing it!

 

[allandwf]

Yes, but your checking everything cold, symtoms appear when hot? An awkward one :/

 

[ledlights]

I would have thought that if it was a fuel pump issue, a low fuel pressure error code would appear..... It's how we diagnosed the fuel pump relay before.

The funny thing is the surging on the motorway (with your foot he'd firmly in the same position), anybody had that before?

 

[ledlights]

I've now managed to change the crank position sensor and I've fitted a new gasket (Volvo stock) to the throttle body. I've also checked every pipe and union into the plenum for splits and air leaks - if you suck on each of the pipes there are only a couple that allow air in through non-return valves. Even when these were pinched off, the car still manages to stall from revs..... All of the o-rings have been replaced and lubed with silicone grease and the plenum is as tight as a drum. Any ideas?

No codes showing, and a whole lot of the sensors in the car are now new.......

Does anyone else's throttle body whistle at what sounds to be about 2-3kHz when the car is stopped with the ignition on, or after the engine has been turned off? Mine does....

Thanks,

Steve

 

[EVOeng]

The throttle body whistle is a vacuum leak. When you installed the new gasket for the throttle body did you make sure that the surface was completely clean and smooth?

 

[saintetienne]

My throttle body does a "sonic" whistle also - always has , think it must be the nature of the electronics.

The surging bit is odd - could it be fuel injector related ?

 

[ledlights]

The TB noise can't be a vacuum leak - you only hear it when the engine isn't running.... And it sounds like a loud servo motor drive rather than a whistle. The mating surfaces were also cleaned thoroughly before fitting.

Interesting to hear that you've got the noise too Steve, I was starting to suspect that my contactless TB was duff. I don't know about the fuel injection issue as I don't have any error codes to go from and I've not seen anything else reported.

I've run out of other ideas here.

 

[saintetienne]

Just a thought have you had a fuel filter change ? a lot of main agents even overlook , many cars don't even have it listed in schedule.

 

[ledlights]

Thanks for this - I don't actually know but it gets serviced every year at alfanet services and they're normally pretty good but it's definitely worth a shot, so I'll do it.

Two things I did notice when I had the plenum off was that it's possible to suck air from the small pipe attached the the Newman valve - vapour recovery, I think (one of the ones attached to the back of the inlet) and also from the oil breather that attaches to the side of the inlet. This would allow unmetered air in, so could be a potential leak source.... The pipes aren't split but the valves don't seem to work very well, I don't know if this is normal.

 

[saintetienne]

Not sure about those - might be worth blanking them briefly when car is hot and checking outcome , I had a Golf Gti that had not had the fuel filter changed in 120K and that had full history.

 

[davy83]

I had surging throttle problems and it turned out to be both the pedal sensor and the TB were acting up. To be honest it sounds like your TB is not working properly. I had my unit upgraded by Zmodex in Canada and it does not make a singing noise. The surging could be the pedal sensor, if it hits a worn spot it might jump from high to low and cause fluctuating throttle, however this normally shows up at very low throttle where the pot gets most wear. The vacuum hoses might cause some surging but unlikely to cause the engine to stall. Fuel filter is an easy job to do if you get the urge its behind the lining in the boot at the right hand side of the fuel tank, fixings are simple just make sure you catch any spilled fuel or it will smell for ever!

 

[ledlights]

Thanks for this Davy, I'm coming to the conclusion that my TB is faulty too..... The fault appeared when I replaced it for a contactless one (although my previous TB was faulty for a few weeks before this which gives rise to some uncertainty on timing).

I'll try the other things on the off-chance but as soon as Mike Roberts gets back I'll go over and try substituting TBs to see if it disappears.

Cheers,

Steve