Trottle Problem?
 

I have a problem with my 1990 GT that I hoping to get some ideas on. When I first start the car up it idles fine. I let it warm up a bit, then start driving. When about two minutes later (sometimes less) I'll start having issues with the RPMs jumping around, the engine power dropping off and recovery, and I can even feel it in the pedal. The temp of the engine is at about 1/3 up on the gauge, and battery charge is consistent. When I come to a stop sometimes the issue continues, sometimes it stops. This will continue until the engine is over half way for the temp gauge. Then it will act like a normal, happy GT.

I took it to a trans shop, and they said that I was missing a gromet on the throttle connection (which they replaced) and the throttle had been slipping. Alas, this was not the problem as I continued to have issues this past week, and the shop said that they don't know what's going on with the car. Any ideas?

RE: Trottle Problem?
 

Could be a bad O2 sensor? You'll need a scan tool to check. Read this tread, about what sometime the o2 does:

https://www.fordforum.com/m_2299/tm.htm

RE: Trottle Problem?
 

Sorry it's taken me so long to give an update, but it's taken some time to get this all looked at and a better idea of what's going on. I changed out the O2 sensors, but still no luck. So I had the computer diagnostics run, and it came back as the EGR Valve and the Mass Air Flow not operating. I replaced both (including the EGR Sensor to be on the safe side). The car is definately running better, but hot and I still have the RPM's jumping around at mid-range temperatures. I was thinking that it could be a coolant sensor or thermostat issue or maybe the throttle sensor, but I am leaning towards the former with the temperature gauge being on the high side. Thanks for taking the time to offer options!

RE: Trottle Problem?
 

i have the same problem with my 88 Gt from time to time check your Idle Air Control motor. It happened on my car and that is what it sound like on yours. Only i don't have mass air, i am running around with speed density fuel injection