rough idle

i bought a 1999 grand am 3 weeks ago and already put 1800.00 into it...it idles rough when at a stop sign or red light...rpm is at 500 when idling...i want to know what to check to get it fixed...noone can tell me and i am at my wits end...please help

4 cylinder

So what has been replaced ??
That would help narrow it down a Lot !


and Welcome to AF.

Is it a low idle or a rough idle? Low is usually rough, but rough isn't always low. If you rev it to the desired idle does it smooth out or still run rough at the correct speed?

I was looking through the datastream on my '98, and it said the desired idle was 9xx RPM. The actual RPM was hovering around there and it didn't sound too fast, but it seems a bit high, but who knows...

sorry ... im new to forums...

its a 1999 grand am se...4 cylinder...2.4 ltr twin cam


i was driving it this morning and it idled at 900 and ran much better then i went down the road and it went back to 500 and ran rough again... it drives perfect this is the only problem i am having


thermostat
thermostat housing
water pump
egr valve
catalytic converter
spark plugs
spark plug boots


all the things i have had replaced