RPM sudden surging

akaNYr · Apr 9, 2019

I have a 95 Mustang GT 5.O SN95 with randomly surging RPM's for months. It starts 20 minutes after I start driving. The car don't move any faster but will jerk then bang when the RPM surges kick in, anywhere from 1000 to 2000 above normal. I changed cracked vacuum lines, cleaned the MAS & throttle body 5 times, lubed the springs & cables on the throttle body & cleaned and tested the iac, none fixed it. I tested the (non adjustable) TPS, it wouldn't go below 1.09v throttle closed and 4.85 wot. I bought a new (non adjustable) TPS & it reads 1.38v throttle closed. Car has more power & responded better but RPM's still surge, and NOW when idle RPM bounce between 800 and 1000. I set it for 750rpm. Nov.2018 I got codes 56, 45, 64. I don't have coil packs (code 45). Since then the only code I get is 564 (electric drive fan fault). The radiator fan goes on alot sometimes, the car shakes a little and volts go up. Any RPM help would be much appreciated.

Silver95bird · Apr 9, 2019

Radiator fan acting weird plus surging makes me wonder what shape the ECT sensor is in. Check it's resistance, wiggle it and see if it's steady, check the wiring harness also. If it's failing and going sky high, it'll trip on the fan as a fail safe.

07GtS197 · Apr 10, 2019

Do you have an auto? It sounds like its downshifting. But the idle rpm bouncing wouldnt be related. Ect is a great place to start. Does your smog pump work?

Sent from my iPhone using Tapatalk

g36 monkey · Apr 10, 2019

I know you said you replaced some vacuum lines. I would always start will a good vacuum smoke test.

ttocs · Apr 10, 2019

and there are a ton of vids on youtube that show easy ways to do it

akaNYr · Apr 12, 2019

Thanks guys for all u r advice. I'll check the ECT and harness. It is an auto tranny and I have no smog pump. Cars over 15 or 20yrs old don't get inspection. So now 3 people have told me to do a smoke test. After I got my car back from the garage that did the vac lines I had a feeling everything wasn't on the up now up with this guy. ECT, harness check n smoke test it is. I'll fill u guys in when done.

07GtS197 · Apr 12, 2019

I would say that one of your problems is either a bad or misaligned mlps. One common sign Ive seen is the trans falling out of overdrive at highway speeds.

Sent from my iPhone using Tapatalk

summerstang95 · Jul 31, 2019

akaNYr said:
Thanks guys for all u r advice. I'll check the ECT and harness. It is an auto tranny and I have no smog pump. Cars over 15 or 20yrs old don't get inspection. So now 3 people have told me to do a smoke test. After I got my car back from the garage that did the vac lines I had a feeling everything wasn't on the up now up with this guy. ECT, harness check n smoke test it is. I'll fill u guys in when done.

Any luck on getting the problems fixed? Mine is doing the same thing.