I just got my 91 monty a couple of weeks ago. When I got it both the check engine light and service engine soon light were on. It idled a little rough but nothing major. I took it to a shop just to see what was up with the idle. They looked it over and told me I would have to change the 02 sensor and thermostat before they could really get in to diagnosing it. They told me a high price for changing those two things so I payed them $100 for their time and took it to another mechanic. The next mechanic put the 02 sensor and thermostat in and then noticed the radiator dripping. Took out the radiator and replaced with a new one. That totaled me $550. Got it out...started it up and then it idled more rough then when I first brought it to them. As it sat there idling rough the mechanic unplugged the air flow meter and bam...good idle. He looked at me and said "your air flow sensor is bad". I found a good used one and had it shipped to me. No way was I payin $800 for a new one! WOW! Okay...so I undid the battery and plugged in the new air flow meter...reattached the battery and fired it up. My service engine light was gone and the car seemed to idle fine...for a minute...then it started gasping and trying to die...once I got it warmed up it held idle but seemed rough still. I got out and unplugged the airflow meter again and boom...good idle again. Started reading a bit and came across others with the same issue always hoping they would post what ended up working but no one ever did. I found posts that said it was the throttle body so I cleaned that too. Still...nothing better. I haven't gotten it out for any long drives but after it's warmed up every time it seems to be fine. It's just that initial cold start. Fires right up...holds idle but pretty high and has major gas smell...pump the gas for a minute and then starts to idle better. Not great...just holds... probably 1100 rpm. I love the look and feel of this car and want badly to keep it. Can anyone help? I'm not a mechanic at all. This is about as in depth as I've ever been with a car. HEEEEEELLLLLLLPPPPP okay...just took it out for about an hour. Started it up and went through the same process it always does from cold then took it out on the highway. It ran fine on the road but sucked a lot of gas. Got to a friends house. Turned the car off and went in for a few minutes. Came back out and started it up. Seemed fine so I took off. City driving. Stop and go stuff. At each stop light it tried to die so I had to pump the gas to keep it goin. It would sputter and then lunge and start running okay. Next stop light same thing. Got back to my friends and turned it off. Got out...smelled gas. Waited for about an hour...got in...started it up and went through the same cold routine. Then took it out on the highway ran fine. Got it home...pulled in to the garage and turned it off. Got out...smelled gas. I have no freaking idea!!!!! Help please!!! Sorry for the length of the post. Just trying to be thorough.

 

the PCM in that model was NOTORIOUS for going out, usually just wont start, but have seen soo many senarios of odd symptoms for a bad pcm. idle spped control motors were also a common issue. both unfortunatly are pretty pricey. check engine light codes for a bad pcm are usually injector codes, if you have a scanner look at the data in the mfi section. all sensor readings will be WAY out of wack, but the engine still runs.