Oldsmobile Aurora Engine Misfire And Rough Idle

1999 Oldsmobile Aurora. Question: my 98 Olds Aurora seems to have a misfire. I just changed the spark plugs and wires last year and i checked all the coils (checked the spark plugs and wire as well) but all seems to be in order.

I cleaned out my egr valve but it made no difference, the check engine light comes on from time to time but it goes away after some time. The car seems to idle rough more when its in gear than when in park. Sometimes if i don't put it in neutral at a light it will stall out, furthermore it seems to be affected more when the heat or a/c is on than when its off. There is a definite misfire it can be felt under acceleration and at all stops. As I said all the plugs, wires and coils are good.

What else could be causing this problem?

ANSWER:

The next step is to have the system scanned for codes. Most of the large national parts store chains will do this for free. The codes(s) will give some direction as to where to focus on repairs. Sticking injector is a possibility.

A Vacuum leak may also be the problem. Vacuum leaks cause a lean condition so the engine module will try to compensate by making the fuel delivery more rich. The idle worse in gear than not, could be a worn engine mount. Even if the engine is running properly, a worn or broken engine mount will cause the normal engine vibrations to transmit into the frame and body of your Oldsmobile.

Sounds like you could have several problems. As first stated, you nneed to get the system scanned for trouble codes to know where to continue diagnosis.

Question:
2001 Oldsmobile Aurora. Will a bad throttle position sensor on my Olds Aurora with the northstar v8 4.0 cause it to run at 1900 RPM? It wont idle any lower. At first it would idle back down if i tapped the throttle. Now it is stuck at 1800 RPM.

Answer:
Yes, a bad TPS sensor can cause your idle problems, but there are two other more common causes.

1. The throttle plate and bore are full of carbon and the plate cannot close all the way allowing too much air to enter the engine. Clean the plate and bore then take for a ride and blow it out real good.

2. Most common is a vacuum leak either between the throttle body and upper intake or the upper intake manifiold and lower manifold. These items have rubber gaskets that over time shrink and cause a vacuum leak. Sometimes with this condition the idle will come down after the engine warms up and the gaskets swell up and seal a little better.

A vacuum leak can be tested by spraying a little carb or brake cleaner around those areas to look for an RPM change. Be carefull to stay away from any source of ignition since the sprays are very flamable.