Sam H.

Can anyone help with a diagnosis? My '88 S4 usually ides nicely at about 850 rpm. But today, it's idling just enough to keep running, like 100 rpm. When I increase rpm, it runs and sounds ok, but it will stall when I get off the gas.

Battery guage seems a little lower than usual. But the car always starts. What are the first things to check?

Thanks for your help.

SeanR

I'm having the same issue and am leaning towards the vaccume system. I've only had it die at idle (coming to a stop light) a few times and am going to go through the vac sys first.

If you find out what the issue is, please post it here.

Fishy928S4

ISV?

Mrmerlin

Hi charge the battery then open the air cleaner box and look under it for a vacuum leak at the 5 way splitter also check the fuel pressure regulator and fuel damper for fuel leaking into the vacuum lines and any other loose connections like a loose MAF clamp after doing this stuff the battery should be charged, also check the temp 2 sender plug for the wires shortign together this is on the front of the intake with the blue connector mine were shorting together so i had to replace the plug

Sam H.

Can you experts help with a diagnosis? My '88 S4 has always idled at about 850 rpm. Now, when I start it, it starts fine, then barely idles at about 100 rpm. When I increase revs and then let off, the car stalls.

Garage smells of unburnt fuel. Must be ignition, right? Coils? Something else? I appreciate your help.

Lizard928

start by checking plugs, check wires resistance, inspect cap and rotor, swap with a known good MAF from a good running car if you can.

Mrmerlin

Hi it sounds like LH failure, do a search for more info in FAQ section

Bill Ball

I'm with Stan. This is almost the same failure mode I had. Find a friendly local 928 owner with MY 87+ who will allow you to swap LH brains. Easiest for him would be to remove your LH and see if it makes his car run the same way. You're probably going to have to remove yours anyway.

Certainly go ahead and check for good spark at each cylinder first and rule that out.

Sam H.

Thanks, gentlemen. I'll take your advice and focus on the LH brain / MAF for now.

S4pilot

I'm with you guys on this.. I think LH unit also. I had a similar problem and Rich rebuilt mine.

Tony

O2 sensor...its the cheapest thing to start with. I just went through this. I had a spare MAF and it made no change. Wouldnt hurt to try before a new LH!$$$

Bill Ball

The O2 should be a maintenance item for any car over 100K miles, but don't expect it to fix this. My car idles fine w/o the O2 sensor attached.

fabric

Sam-

Here's my attempt at a guide the the stuff Stan mentioned, plus a whole slew of other stuff that can possibly affect idle problems. It's for an S4 specifically, but conceptually same for others. If you don't have a vacuum tester yet, now's the time to get one.

http://members.rennlist.com/fabric/i...eshooting.html

BC

Lagoon Green Metalic S4 in San Diego. I think I have seen you driving - around Poway possibly?

I don't have an LH handy, but if you needed any social support, I would like to help in anyway. I am in Penosquitos, and my office is in Solana Beach.

Bill Ball

If Brendan's LH is already out of the car, then it is a 2 minute job to plug it into your harness and see if it resolves the problem.

Also, you could unplug your MAF as a test and see if the car runs better. If it does, then the MAF is suspect.