Hi i have a 97 monte carlo with a 3.1 and the idle is rough. When you use to start it and it idled it use to be at like 1000 rpms and now when your idleing it moves from 1000 to like 500 over and over until you give it gas and rev it up. But when your driving somtimes when you go you can hear a quiet knock over and over until you get like past 5 or 10mph and it stops and the car runs perfectly fine and the rpms are fine not until your at a stoping or taking off idle but that quiet knocking i hear by the egine is only somtimes, seems like the issue is getting worse i think also when you take off from a stop it hessitates to go somtimes and putters but once you get speed its like nothings wrong and thats always. you can hear the muffler make a putt putt putt constaly when its parked and idling. Just curious if anyone could help me and let me know on what to do . there is no check engine light on either. thanks for the help.

 

It could be a lot of things. When was the last time you changed the spark plugs, wires, air filter, fuel filter? You may want to clean out your IAC and EGR valves to see if it will help any.

 

i checked the front three spark plugs an there all fine and the wires are still good. Air filter does need to be replaced but its not that bad and it wouldnt cause the car to do whats its doing so bad. Where is the IAC and the egr valves? also when the car idles down the lights dim as well.

 

Or the idle motor.

 

ok well ill look into the egr valves and the iac which i think is right at the throttle body. thanks.

 

Don't bank on all your plugs being good just by checking the front 3. I changed all my plugs the day after I bought my car and found out the previous owner (or someone) that had it before changed the front 3 but not the back 3. It kinda pissed me off cuz it's not hard to do, so for your sake and the car's.... Check em all anyway so YOU know for sure. Just thought I'd add my 2 cents on that part. About your main problem, it could be many things

 

Could be the catalytic converter, if it's clogged it definitely hurts the car's acceleration, not sure about idle though. Maybe your exhaust has something wrong with it too, best bet would be to take it to a shop and ask their opinion.

 

ok, you should start with a tune up, also look into a new fuel filter. i had a similar problem, you definitly wanna clean the IAC & EGR valves, very simple to do. also look into a throttle position sensor ( TPS ), possibley the o2 sensor, or, worst case scenerio, a catilitic converter.... other than that, the tps is around $20, fuel filter is like $20, EGR cleaner is like $6....

if it has the service engine soon light on, ( or any lights on at all) take it to advanced auto & have em pull the codes for free. in my case, i did a tune up, tps, cleaned the egr & iac, & an upstreem o2 sensor... the o2 sensor was bad, it caused all kinds of other problems with the PCM trying to compensate, now it idels much better....

 

well if it was an o2 sensor or any of that wouldnt my check engine light have to be on. there is no check engine light on but its my other car im just working on and i havnt had time to work on it much so i have not done much. also if i wana do a tune up which i dont think i do bec my front 3 plugs n wires are fine and my car does not misfire or mis at all just a rough idle dont i have to pull the engine to do a tune up since the other 3 are way tucked back behind it all?

 

Just roll the engine forward.