Idle issues and Lambda light 1996 850 GLT N/A

[Herving]

have a 1996 850 GLT automatic non turbo its my dads car that he doesn't care for but i want to keep it running. I was hoping someone would be able to help with some information on an issue I'm having.

It has an issue where it will rev up above 1000 rpm and then drop down to 500rpm or bellow, then it will continue to go up close to 1000 rpm then down. Sometimes it dies when going down. this will happen randomly, sometimes off cold start, sometimes after driving for a while etc. sometimes i can go a whole drive without the issue. its idle rpm is a bit high, close to 900 rpm but it does have the Lambda light on ( i suspect something with the exhaust but i will get to that soon). I have cleaned the OEM idle air control valve since it was very filthy and that seemed to help the issue, after driving the IAC would become extremely hot and i thought maybe that was from a short in the internal electrical. I bought a aftermarket IAC online and it seemed to be working better the issue went away for a bit. But the issue seems to still happen randomly although not as often. the aftermarket IAC still gets extremely hot after even a 20-30 minute drive.

More about the exhaust and lambda light: the exhaust is very rusted, it was redone quite a while ago(10 ish years). but i don't think the cat was replaced and the mechanic that did the exhaust was a bit of a shmuck. I have a few thoughts about the exhaust being connected to the lambda light. possibly the O2 sensor needs to be checked/replaced. Maybe the cat is clogged and that's causing some issues. I know the exhaust is rusted and has some leaks, that is after the cat, but that could also be contributing the lambda light.

More about the idle and revving: some more things I've noticed is the idle will rev up about 1500 rpm when going from drive(brake pressed) to neutral. lets say i come to a light and i hold the brake down in drive, the idle will be around 700-900 rpm. if i put the car in neutral while stopped the rpm will shoot up around 1500 rpm. the same happens when you go from drive to park idle will be close to 700-900 rpm and once put in park it shoots up to 1500 rpm. takes a minute or two to drop down to 900-1000 rpm where it will stay.

another odd thing about the idle. one time after a start up the idle was sitting around 900 rpm and it then started to do the issue of revving down and up. when it would drop down the transmission light would turn on until the rpm went above like 500 rpm. another time while driving the transmission light was flashing and when coming to a stop the transmission wouldn't down shift to 1st gear. the car had the transmission rebuilt twice about 10 years ago. first it went when driving on the highway just out of no where, it was rebuilt but shortly after the transmission light started flashing and so my dad brought it back and after some work they said coolant was leaking into the transmission. so it was fixed again.

Further more when working on the car myself with an old friend who is a mechanic we were checking around the throttle body/ intake area. we noticed the hose that connects from the crank case to the flame trap into the air intake was really not secured well(possibly from previous shmuck mechanic) we thought that could have been causing the lambda light and vacuum leak. we kind of mcgievered a solution so the flame trap would be more secure. I did a glove test to check the PCV and it did fail which is expected because the whole PCV system was never redone.( might do that at some point,)

The issue is random. unfortunately i don't have a scanner that can pull codes but I'm looking into getting one maybe that will help with the lambda light and such. hopefully someone can help with some info it would be much appreciated.

[misha]

Try with disconnecting the Maf sensor first.
If it idles better with Maf disconnected,you found the culprit.

Dtc codes must be read to see what exactly the problem is.

[Clemens]

other than that, it could be an dirty Idle Air Control (can be cleaned), or a vacum leak.