: '94 SLS Idling to fast

09-18-06, 11:36 AM
My '94 SLS is Idling way to fast, around 1800 rpm. I changed out the idle speed motor, with no effect on the problem, I checked the vacuum lines, they look ok.
any suggestions?

thanks for your help.

09-18-06, 11:58 AM
Is the throttle body clean? (blade not closing all the way)

Generally if you have a high idle and can't find it.. it's usually a vacuume leak somewhere.


09-18-06, 12:11 PM
I will check it to see, also, I will check the intake cover for leaks, that is one spot I did not check.

09-18-06, 12:16 PM
Check around the top of the throttle body on the vacuum line "boot". That seems to be a common problem place

09-18-06, 01:28 PM
Vacuum line boot? would that be the location where the 2 vacuum line tubes come out?
also, would one of the green rubber seals around one injector being half gone cause this problem?

09-18-06, 02:35 PM
Yes, and maybe.

I think because the injector is inside the manifold, that the lower seal doesn't really seal anything. But I would get it replaced anyways, they're cheap.

09-19-06, 10:00 AM
I pulled off the top of the intake, all looked ok, then I re-installed the top and still it idles to fast.
I checked the vacuum lines at the top of the throttle body, they were ok, and I went ahead and checked any vacuum lines I could find, still idles to fast.
Could a bad Fuel Pressure Regulator cause this?
Fuel pressure seems to be about 45psi, and the needle is solid steady, with the car running, not pulsing up and down.
does this indicate a bad FPR?
again thanks for the help.

09-19-06, 11:10 AM
Does not sound like a bad FPR, but why didn't you check it when you had the cover off? Sounds more like a vacuum leak (maybe around the cover), sticky throttle plate or a bad ISC motor (I think the '94 used the ISC motor).

09-19-06, 12:04 PM
How do you check the FPR with the cover off?
throttle plate looks normal, but I did not look at it close, I will re-check it.
I replaced the ISC motor, and it did not help.
I might have to take it to a pro.

09-19-06, 01:01 PM
With the cover off, turn the key on to pressurize the fuel system, but DO NOT start the engine as it will run away WOT and bounce off the rev limiter. Now look for fuel leaking from the FPR nipple. There should be none.

Did you adjust the ISC motor after replacement?

09-19-06, 03:00 PM
I set the ISC to the same distance as the old, but it is more likely set shorter, which is pushing on the throttle less.

09-19-06, 04:09 PM
But did you use the correct proceedure to set it? You have to push on the plunger with your thumb. The plunger will retract. When it bottoms out, pull the plug and adjust it to .030 gap with the throttle linkage, then plug it back in.

09-20-06, 10:32 AM
I guess I did not use the correct procedure, I will re-check that adjustment.
I checked the FPR with the cover off, and it was ok.
still idling to fast after the cover was put back on.

09-20-06, 11:00 AM
Have you checked for codes? You might have some sensor problem causing the engine to idle higher than it should. TPS comes to mind.

09-20-06, 11:24 AM
I read the codes through the instrument display after holding down the OFF and warmer buttons at the same time until it went into the test mode.

09-20-06, 11:27 AM
One thing I have not checked is the gasket between the intake and the heads, is this a possible source of the idle problem?

09-20-06, 12:10 PM
Not too likely. A vacuum leak where the top intake cover seals is much more likely.

09-20-06, 12:49 PM
I read the codes through the instrument display after holding down the OFF and warmer buttons at the same time until it went into the test mode.


09-20-06, 12:55 PM
No codes were found.

09-20-06, 01:08 PM
No codes were found.

That suggests:

First, with at idle at 1800, you should have a P030 - ISC RPM out of range code. Since you DON'T have that code, that suggests that your PCM doesn't know it's idle.

This could be because you did not set the proper clearance on the ISC motor, so that the switch isn't contacting the throttle body. Another possibility is a wiring fault on the switch wiring.

Again, it's also possible the throttle position switch is out of range, but usually a P055 would be set...

First, I would try disconnecting the battery, reconnecting it, doing the ISC procedure and letting it idle for a bit. Then recheck for codes.

09-20-06, 01:37 PM
I will give it a whirl.

09-22-06, 01:33 PM
I adjusted the Idle Control Motor, and it did idle down, but it was still to high,
so I took it to the dealer and they said that it had a mechanical bind that was keeping it from idling correctly.
They took off the throttle body and clean and worked the linkages and now it idles correctly.
thanks for all of you for your help.

09-22-06, 02:13 PM
Ask them what was binding. If it was the throttle cable, you might consider buying a new one for peace of mind. Don't need it sticking in the open position. ;)