1999 Chevy Malibu engine shakes & poor idle after head

TJN747

MEMBER
1999 CHEVROLET MALIBU
6 CYL
FWD
AUTOMATIC
207,000 MILES

I have a 3.1L that was overheating due to a bad head gasket. I purchased a head gasket kit and decided to do the repair myself. We (my father and myself) tore the engine down to the block and replaced the head gaskets, and every gasket to that point.

As we put it back together, we somehow got the pushrods on the #2 cyliinder swapped. So after completion we started the motor, It made a horrible banging noise and shook the engine. Exhaust was also coming out the firewall side of the engine (opposite of the pushrod mishap side).

I then tore it apart again, to find the exhaust pushrod snapped in half and the rocker arm cracked. I ordered and replaced both damaged parts, and put the thing back together again.

This time when I started it, it doesn't bang, but the engine still shakes back and forth about 2-3 times a second. It also won't stay at a even rpm at idle. It goes up to 2000 rpm and then goes down to 200 or so (almost dies) like a small engine that is surging. Exhaust still comes up from the firewall side of the motor, from a much as I can tell, it seems to start at the bottom of the valve covers.

I've tripled checked all the electrical connections, proper spark plug wire routing, and vaccum and breather tube routing.

I'm getting to the end of my rope with the project and hope someone can help give me some ideas on things to check.

Thanks in advance, TJ

2 Replies

HMAC300

MECHANIC
48,600 POSTS

First thing to do is a compression check. There is a good possibility that you bent a valve due to one pushrod beeing longer thatn the other on these engines. If you find the compression bad then it will have to come apart again on the side with the low compression and fix the valve. If compression is ok, then put a vacuum guage on it to check what the vacuum is as it could be a leak. Also the pcv vavle hose tneds to break right at the throttle body on these due to those being plastic at that connection so check for a vacuum leak there. Also the cylinde that had the snap, chec the spark plug to see if it's closedand may need regapping. YOu'll need to pull it anyhow to chec compression. It really sounds like you bent a valve.