My car is having a very erratic idle along with stalling or almost stalling when coming to a stop. Not sure it it's quick stops only or all stops. It will idle fairly high, up from the normal range of 500-550 to 900 or so. It usually seems to be hunting too, up and down a bit, but not all the time. Rarely, it idles fine for a short bit but that is temporary and can happen once during a drive, a couple times or not at all. The person that regularly drives the car has complained that its smelling from gas too. Another possibly related issue is the gas tank pops in and out, probably due to a bad vent on the tank.

A year ago I replaced the throttle body, cannister, cannister purge valve TPS, IAC, and some old damaged dried out plugs. Everything ran perfect before the repair and after the repair up until about 2 months ago when it started to idle a bit fast. Nothing terrible, but a bit fast. Since then it's gotten worse including stalling and almost stalling when stopping or stopped and the other problems listed.

I pulled off the IAC and it looks ok as long as fine includes an extremely light coating of a blackish brownish dust. I replaced the purge valve again as the one I replaced last year has some kind of gunk build up coming out of the edges. Fuel related I guess, but I'm not sure why its happening or if this is even related to the idle issue.

There are no codes and haven't been any. I've checked as many vacuum hoses as I can easily see and those seem connected and fine, not to mention that I replaced many of them a year or so ago(along with a check valve that's right near the map sensor) due to age, except the one from the vacuum storage ball thing in the fender to the "junction" at the top of the wiper fluid reservoir due to it being difficult to get at. Brake booster and pcv hoses were changed as well as the hose going from the TB to the passenger side valve cover last year.

I'm at a loss as to what to check now. Can anyone give me a list of things to do/check?

Also, I have the cables and software to do datalogs but I don't want to just do those and toss them on here unless someone asks me to as I don't even know if they would help. If a datalog is suggested, tell me how long it should be and what I should "do". i.e. drive normally for 5 minutes or let it idle for 10 minutes or rev it occasionally, etc.

Tonight, when the car was driven home and put into park outside the house, it was idling perfectly normal at about 500-550 with no hunting, although the drive from work had the same issues as listed earlier.

 

Sounds exactly like what my car was doing before the headgasket blew. For me, it was diagnosed as a bad distributor.