91 mtx running very rough

[WhiteSHO91]

My 91 mtx will start right up and idle fine for about 25 seconds but once I try to drive it anywhere it surges very badly and won't rev past 3k rpm. Even while going down the road at a decent speed the engine will surge and almost die making the car lurch and shake pretty bad. I've replaced the ICM, cam position sensor, fuel filter and cleaned the MAF recently. The colder it is outside, the worse this problem is. I have an aftermarket air filter on my car and the IAT is still sitting in the bottom half of the old box so maybe that could be a cause? Any help would be appreciated.

 

[luigisho]

What do you mean it's sitting in the bottom half of the old box? Is it not running with an IAT in the system? when I had an aftermarket setup I think I plugged the IAT somewhere in the intake setup. Check the car for stored codes. I would also unplug the MAF and see if it runs any better. Not runs great but stops surging.

 

[jimtash]

You need to install the IAT. Sound like the coil pack might be acting up.

 

[WhiteSHO91]

I did try unplugging the maf and it made no difference. so I should try mounting the iat somewhere near the maf?

 

[SHOdded]

What did you use to clean the MAF? Not brake/carb cleaner, I hope. That would def **** it. No change after unplugging the MAF usually means it needs cleaning or it's toast. Have you checked the wiring to the sensor to make sure it's not shorted or broken or (continuity/resistance) ...

 

[luigisho]

First thing. Pull your codes. The answer is most likely in there.

What is your intake IAC setup? You have to be very precise when you explain things so anyone reading and trying to help knows what you are talking about.

 

[WhiteSHO91]

i used maf cleaner on it. my curremt intake setup is all stock with a cheap cone filter where the top half of the stock air box went. the iat sensor is still in the bottom half but im going to mount it near the maf when I get the chance. im not getting any codes when I hook up my scanner and it is an obd 1 scanner.

 

[WhiteSHO91]

if I get a junkyard maf does it have to be from a sho or will any ford 4 wire maf work?

 

[luigisho]

You need to get one calibrated for the car. Look around for parts cars in the classifieds ebay etc

 

[Devin]

You can't accelerate past 3k? Could be the TPS (throttle position sensor). No codes is strange. No CEL (check engine light) illuminated?

 

[itwonder]

I would check stored codes, and run KOEO and KOER tests to diagnose.

 

[WhiteSHO91]

the cel will flash for a half second when the car "dies" and will go back off when the rpms come back up. but the car never actually stalls, its almost like the key is being turned on and off very quickly. but it seems to run and die on all 6, not misfiring.

 

[luigisho]

I think some obd I scanners don't work properly on the system for some strange reason. Try the paperclip jumper and see if you get anything. http://web.archive.org/web/20090917070939/http://www.shophoenixproject.com/eec/eec.htm