Brittania

newbie 951 owner , got a little problem with deceleration. As I take the foot of the throttle and the car starts to decelerate I get a little stumble down towards the low rev's around 1700 - 18000. Its not smooth. Especially when warm the problem gets more intense. At low speed it seems the car stumbles around . I have an air fuel meter and can see when the car is getting fuel. Looks like the idle doesnt come on in closed throttle until 1800 rpm and when it does come on its jerky. . I have to put the clutch in to avoid stumbling. I checked the TPS, it makes the clicks on open and close.

Should the idle come on as soon as the throttle is closed or is it programed only to kick in at low revs. I'm thinking the TPs may be bad?

Need help

Tom M'Guinn

I am not certain I fully understand your question or your symptoms. However, if it helps to know, the computer is programmed to turn off the fuel injectors above 1600 rpms when the TPS is in the fully closed position. This saves gas and let's the rpm's return to idle sooner than they otherwise would. I think you may be seeing this on your a/f gauge, but am not clear.

Is the stumbling/jerkiness only happening when you completely lift off the throttle, or does it happen under light load too? Low rpm stumbling could be a number of things, including vacuum leaks (!), aged air flow meter contacts, or more vacuum leaks, or other things.

Brittania

It only seems to stumble when I'm off the gas. As the car decelerates and the revs drop the stumbling starts. This is more noticeable when the engine is hot. Thsi ahs got me stumped.

fast951

Few things to check:

- Make sure your Throttle plate is closing all the way (check the cable).
- Is your car running overly rich?
- Do you have a vacuum leak?
- Is your Blow Off Valve working properly?

Check the basics...

Brittania

Thanks mate,

I'll be checking this out tonight.

Whats the best way to check the BOV ?

She does run a little rich, no sign of black smoke but the tailpipe is very black.

Cheers

RajDatta

John, I think you might have hit something that I might be experiencing. When I get off the gas, I get a sumble sometimes before it evens out. Also, my idle is a little high at 1000rpm when warm but is perfect at 850-900 when cold. I did switch to 52# injectors but kept the same chips. The car initially came with stock 944 turbo injectors with 3.8 bar 968 FPR. Now I have the FP dialed back to 2.5bar at idle.
These are some of my mods, 3.0 shrtblk, 2.7 head, APE/PH MAF, K27/8, 951S dme/klr.
Am I suffering a similar problem of being too rich at idle?
Thanks
Raj

fast951

Brittania, Check your fuel pressure, your fuel regulator can be bad and causing over rich condition

Raj, If you are using 52# injectors with chips designed for stock injectors, then you AFR is very rich... WARNING you could even damage your engine by washing the cylinder walls. I'm sure you have plenty of $ in the engine, get it tuned correctly and enjoy it.

It appears that the original 3.8bar FPR was a bandaid solution..

Brittania

Already replace the FPR. She was blowing black smoke before it was replaced, Fuel pump was noisy - the usual symptoms.

Mike951

Pull the vaccuum line off the top of it and put a vaccum tester on it. It should not leak.

Chas

Replace your TPS.....I have the exact same symptoms, and it cleared up with a new TPS.

My symptoms were the same....idled nice and low on cold start, and wouldn't stumble when decelarating. When warm I would have a high idle (1,400rpm), and decelaration would be downright jerky...

Brittania

THANKS MATE, I'M GOING TO TRY ADJUSTING IT FIRST AND THEN REPLACE IF NO IMPROVEMENT.

v944god

I heard of stock chips doing this sometimes.

When people upgraded the chips they lost the stumbling.

Brittania

ALREADY GOT CUSTOM CHIP, THANKS