I own a 1998 Ford Escort ZX2. Ever since I bought this vehicle, it has had a rough idle. I was told by multiple mechanics and some research on my own it is due to where the engine is placed and there was also a TSB about it put out from Ford. I originally had to put in a lot money in this car, way more than it was worth to get it to a decent running condition.

Recently, I had an engine light come on and noticed my car was idling even more rough than usual. I got it read and it was 1506. I had the IAC cleaned, a brand new MAF, replaced the PVC valve. I had the computer reset and the light didn't come back on for another two or three months. It was the same code again. However, it shortly went away by itself the next day or so after I got gas.

It hasn't returned yet but my car has gotten worse. Anytime I start it cold, the RPMS will go low and it will chug along until I press the gas and take off. It has died on me a couple times at a stop light when I was just sitting there and didn't give it any gas. It has always been a little stuttery when doing a cold start but it wasn't ever to the point of it dying or stalling. It is completely fine while driving, its just the idle I'm concerned about it.

I recently replaced the IAC and with this new IAC, my RPMS went haywire and was going crazy, surging like crazy. It shot up really high and so I turned it off and put back in the old IAC. Whenever unplugging the IAC, the car stalls, which I think is supposed to happen.

Can anyone tell me why my car would act so crazy with a new IAC? I'm thinking I probably have a vacuum leak but would like to know what would cause my RPMS to go so crazy with a different IAC.

 

Assuming its got no lean/rich mixture codes, look to a worn throttle body. If TPCT (tps closed throttle voltage, an internal measument of the PCM taken at KOEO when the key is turned on, before it's cranked) and TPS voltage (the realtime measurement) dont match within a couple of tenths of a volt consistantly, these driveabiltiy problems will occur.
If you look inside the throttle body and see scraping, that's a very good sign. Also, if you wipe the dirt out at this point, it will probably make things worse, as the wear dimensionally changes that base amount of airflow.
As for the rough running, that was kinda a real bitch with these cars. If you replace the mounts, it might improve, at least a little. It depends on how much you want to chase it.

 

Nope. That is the only code I had, P1506. I believe I had the throttle body checked out. I will look again though and see where that leads me. Would that cause my car to be stalling and what not?

Also, what about the new IAC? Any ideas as to why my car would react like that?

 

I didn't see much in my throttle body, no scratches or dirt. I have noticed something though when messing around. My AC compressor won't kick on, but when I put the AC on, my RPMS go up like they should and my car runs a little bit better and doesn't feel like it's going to stall as much.

I sprayed some carb cleaner around all my vacuum lines and really couldn't find any leaks.