Rigel7

Hi there,

My '87 928 S4 has recently started running rough on cooler mornings. Once warm she runs like a horse, but when cold she stutters on very little accelerator pedal movement.

I did some research, and folks have commented that it could be the cold start valve malfunctioning. I looked on parts websites for the replacement, but I can't find one for the '87... Seems they only go up to '84??

Is it just me, or is there not a cold start valve applied after '84? - If not, what is the equivalent in the later years?

Thanks,

Marcus

Airflite40

there is no cold start valve after 1984 for US cars. only k-jet and l-jet cars have them. your S4 is lh-jet. the warm up enrichment is programmed into the brain. i am not that familiar with lh cars, the common answers to lh problems are:
could be tempII sensor
unplug the MAF and see if that changes the way the car runs
swap in an MAF from a friends car
swap in a lh brain from a freinds car
if it runs fine after warm up i would suspect there are no vaccuum leaks, so most likely the tempII sensor since the brain doesn't know the engine is cold and feeds it fuel like normal, which would explain why it runs fine when warmed up.
try searching for 'rough start S4' as this has been discussed many times before, also check greg nichols' site http://nichols.nu/tips.htm
im no lh expert, so maybe someone else will chime in

FeedNfrenZ

My 85 ran like that when I first bought it. I can't say EXACTLY what I did to fix it but what I did was pull off the intake and replaced all of the vac. lines, hoses, ect. plus I cleaned and oiled the idle stablizer. Check your vac. junction connector (spider) up against the fire wall around the MAF. My 90 actually had an unseen crack at one of the forks. Do the WD 40 down the Vac. line trick on the idle stablizer. It may be sticking when it's cold.

ZEUS+

All are great suggestions,if they check out fine take a look at the check valve at your fuel pump.

John Speake

When the engine is cold, the O2 loop is ignored and the LH ECU is running purely on MAF accuracy

How many miles on the car ? If more than 80k miles then the MAF is a good possibility for this problem.

Does the car idle at 675rpm when hot ?

RDS928S

John,

don't know if you know-but you were referenced in the latest "Porsche & 911 World" mag. Article on what it takes to keep a 928 running.

Rich

khalloudy

Check your Temp Sensor II. Mine had a problem that exhibited only during the cold. I think i would change it. I have an 87 S4 too

John Speake

>>>>>>>>>>>>
Hi Rich,
Yes thanks, I saw it.... in a couple of months time they will feature an article on one of the few successful supercharged cars in England, with a good mention of the SharkTuner :-)

Now...back to the problem in hand.....