zogster

Happy Thursday folks!

I've just started my '87 944 Turbo up after a few weeks without moving, and the revs at idle are rising to about 2200 within 30 secs of turning the key.

So it's: turn key, engine starts as normal, idles at about 1000rpm for a moment or two, then starts rising, and stops at around 2200.

Any hot tips for where to start trouble shooting?

From memory, I have an idea that vacuum lines or TPS sensor might be places to look.

V2Rocket

try unplugging the idle control valve beneath the intake manifold runners 2/3 and see how it behaves.

951Dreams

I had this problem. When I bought the car it started and ran terrible when cold. Read, really hard to start. I replaced all vacuum lines, and it started great after that.

After that it would do exactly what you describe. I found a PO had the idle screw all the way out. I'm guessing to compensate for an the rotten vac lines. Screwing that back in helped tons.

After that, it would idle at like 700-800 RPMs cold, and like 1100 warm. Before I could run that down and get it all dialed in, head gasket blew. Taking off the TPS I discovered it wasn't "clicking" at idle. Again, I think it was something a PO had done to try and overcome vacuum leaks. Got the TPS adjusted right, but still not back together yet.... So can't report more.

I have heard the idle screw can back itself out. So that's my contribution. Weird to go from normal to 2200 out of the blue tho.

kyle a. w.

My car has done something very similar except it would happen for a couple days and then not again for months or maybe even a year and then do it again randomly. This isn't helping.

zogster

So I tried starting with the idle valve disconnected.

Result: it made a difference.

The revs did still rise a little after startup, but only from about 1100 to 1400. With the valve connected again the difference was 1100 to 2300 today. (I'm putting the c. 100rpm difference from yesterday down to ambient temperature - much warmer out today)

Idle screw, yes, will check that also

951Dreams

So, I'd say your idle valve is stuck. Try whacking it with something?

peanut

not sure how that is going to help with an electrical rotary valve !
It is very easy to remove the ICV to clean it without removing the inlet manifold. 15 minute job tops

It sounds to me like either your FPR is sticking closed and increasing fuel pressure or one of your injector solenoids are sticking due to fuel residue from sitting unused for a while.

Consequently your engine would be getting too much fuel ie a rich mixture as measured by your 02 sensor so your ECU is adjusting your mixture leaner to compensate by adjusting the ICV to allow more air to bypass the throttle hence the rise in idle rpm

I would fit a fuel pressure meter on your fuel rail and see what fuel pressure you have at idle . Check the increase in pressure when blipping the throttle it should be about 0.5Bar
When you switch off make sure that the fuel system is retaining full pressure for 20+ minutes . This simple test will eliminate the fuel pump,non return valve , fuel filter, FPR, and injectors .

951Dreams

That was kind of tongue in cheek. But when I had mine off and was testing it, it was sticking, and whacking it did cause it to unstick, but it would just hang again. A cleaning fixed it for good.

peanut

I tend to whack things when I get frustrated and end up breaking it .

I assumed that the ICV valve worked like a push pull solenoid . It was only when I removed it I realised that it is a rotary valve like a tap (faucet )where the solenoid acts against a strong return spring.

The ICV is controlling additional bypass airflow constantly ,not just as a cold start mechanism. The ECU uses the ICV to add additional air to prevent the engine shutting off at idle like when the alternator or aircon puts an additional load on the engine at idle

peanut

any progress ..............did you check the fuel pressure and leak down ?