: 94 SLS feels like its going to stall when at stoplight



chester_007
03-13-13, 02:21 PM
Hi,

Have a bizzar issue. 94 Seville SLS. 65,000 miles. Runs great and idles nice. Problem arises after the car warms up some. I come to a light and stop. For about 5-10 seconds car idles fine, then it acts like its going to stall, then suddenly surges and levels back out. Rinse and repeat... until it will finally stall. Does not do it out of gear. Does it in all gears forward and reverse. I can simply put it in gear and sit there. Will idle fine then drop and surge back up. I did change the lower crank position sensor because the old one was leaking. It ran fine prior. Could it be the new crank sensor? Or a coincidence? I would have thought that if it was the crank sensor it would stumble and sputter while driving but it runs like a top otherwise..

Thanks!

CadillacLuke24
03-13-13, 02:37 PM
Is the check engine light on?

Pull your diagnostic codes. Those will help fill us in.

How old are the plugs and wires?

chester_007
03-13-13, 03:12 PM
Is the check engine light on?

Pull your diagnostic codes. Those will help fill us in.

How old are the plugs and wires?

No codes or check engine light

Ranger
03-13-13, 05:29 PM
Sounds a lot like a vacuum leak.

stoveguyy
03-13-13, 10:45 PM
I had a sticky egr that caused funky idle for a long time. I could make it stick open real easy. But than I always got egr code too. Different egr and all is well.

chester_007
03-18-13, 12:45 PM
Is the check engine light on?

Pull your diagnostic codes. Those will help fill us in.

How old are the plugs and wires?

No codes other then one for the RF suspension sensor.

Plugs and wires are probably the originals as the air filter was. LOL

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Sounds a lot like a vacuum leak.

Wouldnt a vacuume leak cause and erratic idle all the time? The car idles fine in park and does in drive when you stop - smooth then all of a sudden it drops then levels out again.

CadillacLuke24
03-18-13, 03:24 PM
A vacuum leak can cause an erratic idle. Pop the hood, and with the engine running, use a can of tb cleaner to spray the rubber tubing. If the RPMs increase, you've found your leak. Don't remove the beauty cover, as it's actually part of the intake manifold. If you don't find any leaks, I would think the more expensive chore of plugs and wires would be in order. AC-Delco 91-450 plugs and the appropriate wireset.

Ranger
03-18-13, 04:26 PM
Wouldnt a vacuume leak cause and erratic idle all the time? The car idles fine in park and does in drive when you stop - smooth then all of a sudden it drops then levels out again.
Usually yes.

When was the TB last cleaned?




I did change the lower crank position sensor because the old one was leaking.

Change one, change 'em both. That's like only changing 4 spark plugs.

chester_007
03-19-13, 07:41 AM
Usually yes.

When was the TB last cleaned?



Change one, change 'em both. That's like only changing 4 spark plugs.

Cleaned the throttle body the other day - no help.

I have a set of plugs and going to get new wires - just because I like doing that to all the cars I buy so I know what's what but I honestly don't think its the issue.

I'm personally leaning toward the throttle position motor. The throttle position motor gives the car gas under load to keep the RPM's constant. In park there is no load so the motor would have no work. Driving the car I'm pushing on the gas pedal so same scenario. But, when I come to a stop there is a load on the drivetrain that the throttle position motor has to compensate for right? So say its going bad and it drops the throttle position for a second then reinitializes to proper location. That would explain the sudden drop in RPMs and then the surge of the TPM overcompensating to keep the motor running. I've also noticed gas pedal movement during this time. Yesterday I had my foot on the gas and my left foot on the brake. I felt the gas pedal move when the surge occurs. Didn't dawn on me till yesterday since I'm not a two footed driver...LOL At least that's my theory. I have a spare NS in the garage that I'll pull the TPM off of and swap them to see if there's any difference. I'll let you know how it turns out...

Ranger
03-19-13, 12:28 PM
What you are talking about is the ISC (Idle Speed Control) motor. "Throttle position motor" had me thinking you where talking about the TPS (Throttle Position Sensor). Yes it could be a bad ISC motor (or maybe just the closed throttle switch).

chester_007
03-19-13, 12:57 PM
LOL Thanks. That's what I meant... Got a lot on my mind these days..

chester_007
04-07-13, 05:41 PM
Just a quick note that the idle speed control motor took care of the issue.

Ranger
04-07-13, 10:11 PM
Thanks for the feedback.