1995 Chevy Lumina Rough Idle

AHA

MEMBER
1995 CHEVROLET LUMINA
6 CYL
FWD
AUTOMATIC
120,000 MILES

My Chevy Lumina 1995 idles rough.I have replaced the following with no success: spark plugs, spark plug wires, ignition module, Idle Air Control valve, fuel filter, Fuel Pressre Regulator, PCV valve, all vacuum horses and the transaxle vacuum modulator assembly.
The car starts well when cold but soon the engine has a slight back and forth shake. When I increase rpm to above 1,500 it stops shaking. Sometimes white smoke comes out at higher rpm. When the engine is hot, the car is difficult to start and I have to pump gas to get it started and then it will idle rough for a few minutes and then shut off.
I took it to a dealership and they could not pull out any codes. The fuel pressure when the ignition is on(engine not running ) is 43 PSI and at idle is 40 PSI. The vacuum is 15 PSI. Compression test is within normal limits.
However, the engine runs rich and there's gasoline in the intake manifold. What could be the reason why gasoline is in the intake manifold?

3 Replies

2CARPRO JACK

MECHANIC
11,533 POSTS

Have you pulled the plugs to see if there is any difference in color in them? It may be a bad intake valve or injector. Find the plug that is different in color from the rest, that will be where to start. Do a cylinder leakdown test to see if the valves are sealing. Where is the fuel that you found in the intake? That is normally a regulator that does that. Does the fuel pressure jump up when you rev the engine?

SPONSORED LINKS

Was this

answer

helpful?

Yes

No

Wednesday, June 24th, 2009 AT 2:17 PM

AHA

MEMBER
2 POSTS

Numbers 2, 4, 3 and 1 spark plugs are very dark. 6 and 5 are okey. The fuel collects around the throtle body and in the air duct. The passage to the EGR is usually filled with fuel. Smoke comes out of the EGR when engine is hot. The pipe from the exhaust to the EGR is wet with gasoline. Sometimes, some fluid comes out of the exhaust before the engine reaches operation temperature. The pressure changes to around 47 PSI and then immediately comes down to 39-40 PSI when Irevv. I will do the leak down test and see.

Was this

answer

helpful?

Yes

No

Wednesday, June 24th, 2009 AT 2:57 PM

2CARPRO JACK

MECHANIC
11,533 POSTS

The only time I have ever seen fuel in the upper intake/throttle body area is when the regulator is bad. Remove the vacuum line to double-check there is no fuel present.

Was this

answer

helpful?

Yes

No

Thursday, June 25th, 2009 AT 7:33 AM