Aatos

Hey,

After my rebuild I have rather low idle at 500rpm. I don't think it's a intake leak, since that would result higher idle, correct?

Pretty much everything changed under the hood so I have no clue where to start the hunt. Ideas?

Mrmerlin

does the engine run smooth? my guess is either a vacuum leak or one of the injectors isnt connected or a plug wire is mis routed, also check the coil wires , make sure they are both seated

WallyP

The idle speed should be controlled by the ECU, thru the Idle Speed Valve. Sounds as if your ISV isn't functioning...

worf928

... or it may be that the idle-side of the idle/wot switch has failed and is not signaling the ECUs to control idle. Could be a loose or bad connector at the idle/WOT switch and/or the ISV.

VehiGAZ

Did you replace your MAF too? An out-of-spec MAF can cause a low idle.

Aatos

ICV is a possibility too, but the idle is pretty nice and steady, it's just at 500rpm..

I also verified with stetoscope that all injectors fire so maybe something else (ignition, timing)?

MAF was recently calibrated by John, TPS is new and I verified that it clicks when moving throttle as are knock sensors. Crank sensor or cam timing sensor?

Aatos

We checked diagnostics with vilhuer today, and the EZK reported ~650rpm when the tach showed 500.

The engine (and the crank sensor) was changed, but instrument pod and computers are same as before when the tach used display rpm correctly. Ideas?

Mrmerlin

check the grounds to the coils and the rear injection harness (there are 2, one for each coil and then each side of the injection) Did you replace the hall sensor??

Aatos

Hall sensor wasn't replaced, there's no fault code for it though. Why do you think the engine compartment grounds are related to the tacho? Doesn't tacho get it's rpm signal from EZK? (Which shows the correct rpm when queried with diag.)

John Speake

Did you do an idle adaptation with the tester ?

Vilhuer

No we didn't since there seems to be some issue between tester equipment and Jaakko's S4. Engine wants to die almost immediatelly when LH is connected while its running. This was there before engine change also. What is weird that there were no discrepancy between tacho and Dutch tester software rpm numbers before engine swap.

John Speake

Very strange....... tach does use the same rpm pulse that is fed from EZK to LH (the one that "wakes up" the LH, and tells it to energise the fuel pump, and also uses the same pulse to synch the fuel injectors.

(On an auto this rpm pulse is also fed to the kick down relay.)

Mrmerlin

another S4 owner had idle problems and after trying for weeks to figure things out he finally removed the hood, then in the light of day was one of the injector harness grounds not connected, once done the car started and idled correctly and now runs great

Aatos

More investigation performed. The car idles very steadily, but hesitates a bit on light acceleration.

I checked the plugs. On cyls 5-8 they're are black, while on 1-4 they're nice. Then I checked cam timing with 32V'er. Both cams were retarded (-5/-6) and I corrected them to 0/-2, but since they were both relatively on the same position it doesn't explain the plug difference.

Since distributors are crosslinked, I could rule out bad coil etc ignition stuff.

Since cam timing is ok, and symptoms don't match ignitition, that leaves fuel.

I verified with stethoscope listening that the injectors on 5-8 are firing on idle.
I checked the ignition harness ground points visually, everything looked okay.
I opened and insulated the injector ground wires from the terminals to be sure and removed cyl 5 injector plug.

From what I've read, you not supposed to get any signal to ground when there's no key in ignition.
However, I'm getting very high resistance signal to ground from both leads on the plug.
When I disconnected the connectors on computers the ground went away, so doesn't seem to be in the harness itself.

Here's the pics of the ohm reading and how I measured. The resistance is pretty high so maybe I'm picking up something that's not really there from the LH box. John?

John Speake

I can't read the value you obtained, and you also need to disconnect the the battery ground at the rear of the car to get a sensible reading. But I think this is a "red herring".......and a "high resistance" - say greater than 30k or so is fine.

Different plug deposits side to side could be due to a leak in the exhaust on one side ? The O2 loop will try and keep the combined gases at stoich, but one side could still run richer than the other.

Worth cleaning the plugs and running the car again to confirm that this effect repeats itself......