1998 Pontiac Grand Prix Shake on start-up after sitting ove

ANDERP70

MEMBER
1998 PONTIAC GRAND PRIX
6 CYL
2WD
AUTOMATIC
148,800 MILES

2 days ago I had new wires and plugs installed due to misfires on cylinder 2 under load. Plug on C2 was burned at wire connection, most likely arcing. Prior to having the wires and plugs done, the car would shake for 10-15 seconds, not violently, but noticeably after sitting overnight. This was a recent development that has happened before but gone away on its own. RPMs would remain at normal idle range, no SES light. Felt similar to a misfire while driving. Now that the plug/wires are replaced, shaking continues on start up but I can't get it to misfire under load, and I've tried. Mechanic did mention small amount of coolant in cylinder near the bad plug. I have no coolant loss, no overheating issues, no oil issues, no smoke in exhaust.

3 Replies

PEAR69

MECHANIC
1,482 POSTS

You may have the beginning of a (the common) lower intake gasket failure. Do a compression and leak down test on all cylinders.

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Friday, September 11th, 2009 AT 2:46 AM

ANDERP70

MEMBER
6 POSTS

Already had the intake gasket replaced about 4-5 years ago. Discovered that when there was oil in the coolant. Hasn't been a problem since. Anything else it could be? Head gasket maybe. That's what I thought, but I have no other symptoms and my mechanic said if it is the head gasket, I'll know within a couple weeks b/c it will fail completely.