Stumbling start

Bigplanz · 11-10-2011, 08:43 AM

91 Olds Silhouette, 3.1 V6. On start, hot or cold, the engine stumbles @ 400 rpm and dies. Restart and goose the gas pedal and it catches and idles @ 1500 rpm, dropping to 900 rpm after about 30 seconds. Put it in gear it runs fine. Plugs & wires replaced this summer. Cap & rotor replaced in '09.

What do think I should check? I am guessing the thermac intake system has a component either stuck or sticking. I will try spraying some PB blaster on the damper in the snorkel.

Any suggestions/ideas? Thanks.

polarzak · 11-10-2011, 11:31 AM

If that car has a heat riser valve in the exhaust, I would check to see if it is working properly.

Master of Cold · 11-10-2011, 11:43 AM

I would start with the idle air control motor.

Master of Cold · 11-10-2011, 11:46 AM

Also make sure the throttle body is clean, and free of carbon build-up

cjm94 · 11-10-2011, 01:56 PM

Pull the vacuum line off the fuel pressure regulator and see if there is any fuel they are very common to go bad and leak causing a hard start fouling the plugs a little.

D-rock · 11-10-2011, 04:12 PM

Check vacuum lines, probably all old, dried, and cracked

johnniebravo · 11-13-2011, 09:51 AM

Had that same motor in an 89 cutlass supreme and had similar problems. My problem ended up being the fuel pressure regulator.

Thurman · 11-13-2011, 12:19 PM

Fuel pressure regulator common problem with this motor. Do Not put PB Blaster into the intake system. Use a good "throttle body cleaner" to spray into the intake system after you do get it running and up to operating temp. The throttle body will get a coating around the outer edges over time and mileage causing the "butter-fly" of the throttle body to not close completely at idle. This sends a false message to the ECU and could lead to a "stumbling" problem.

Bigplanz · 11-13-2011, 06:54 PM

Vacuum lines were ok. Air filter needs to be replaced. Underside or the air intake cover was wet with gas. Fuel pressure issue is a distinct possibility as it sounds/acts like it is starved for gas. I will pick up some throttle body cleaner tomorrow.

reelangler · 11-17-2011, 11:48 PM

Check vaccum lines, fuel pressure regulator, and did you gap your plugs?

Bigplanz · 11-19-2011, 09:41 AM

Vacuum lines were ok. I did gap the plugs to spec. I suspect a dirty IAC valve or throttle body. The issue disappeared on it's own for now. It'll be back of course.

reelangler · 11-19-2011, 10:21 PM

Does it sit alot?

Bigplanz · 11-20-2011, 04:37 PM

Runs every day. Short strips though. Nothing over 10 miles total in a day.

Marty1Mc · 11-25-2011, 01:26 PM

I would check the FPR, temp sensor, and throttle position sensor.