Engine Idles rough?

NITRO135

MEMBER
1998 CHEVROLET MALIBU
6 CYL
FWD
AUTOMATIC
100,000 MILES

My friend has a Malibu and he knows nothing a bought cars. The problem I need help with is it starts hard and has a miss while idling, accelerating and even at a constant highway speed. He had just bought this car a week or so ago so I did a tune up and we have replaced the plugs, the plug wires, the fuel filter, the PVC valve, none of this has helped, I have even pulled off all the coils and tested them and they seem to meet the specs I have found for them. We also had the codes ran at auto zone but they did not show any codes, whether or not they did it rite Im not sure. But I am leaning toward a timing problem. Could you maybe give me any suggestions on this matter?

1 Reply

SQM

MECHANIC
6,383 POSTS

Hello,

This issue could be triggered by a vacuum leak.

Inspect the vacuum hoses for any cracks or breaks. Vacuum lines can become hard due to under hood temperature. Which could make it leak as well.
If you do not see any damaged hoses you can continue checking the system using carb cleaner. Start the engine and spray the cleaner around the throttle body gasket. If there is a leak then the engine will react to the cleaner and the idle should increase.
You can check the same way around the intake manifold as well.

Here is a helpful article:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Please let me know of any questions.

Thank you.