94 5.0 Engine surge when shifting/depressing clutch
vengeancecube
03-07-2009, 05:32 PM
Hey folks. I just got this 1994 Mustang GT 5.0. All seems fine except that I'm getting an intermittent Check Engine light after a few minutes of driving. Also when I'm accelerating and I press the clutch to shift, the engine will rev up to around 3000 RPM. Note that I let my foot off the throttle, then press the clutch pedal, then the engine revs up. If I coast in neutral and rev the engine to about 3k, it will hold for a second or two and then come down. The odd thing is, it's ONLY when I'm moving. If the the car is not in motion, the problem is nonexistent. It idles fine when stopped, no roughness. But when I'm shifting up, especially going after 2nd 3rd and 4th gear, the engine will surge when I press the clutch.
I checked the codes from the check engine light and I'm getting a 176 and a 177. The oxygen sensor is reporting both a lean and a rich condition. Could be a bad oxygen sensor. It could also be unrelated to the surging problem. I tried checking for vacuum leaks with a can of carb cleaner. I sprayed ALL around the engine but it never changed idle even a bit. Used up almost a whole can. If it's a vacuum leak I can't find it. It's almost like the throttle cable is getting stuck when I let off it but it only happens when I'm in motion. That doesn't seem to make sense to me. Any ideas?
I checked the codes from the check engine light and I'm getting a 176 and a 177. The oxygen sensor is reporting both a lean and a rich condition. Could be a bad oxygen sensor. It could also be unrelated to the surging problem. I tried checking for vacuum leaks with a can of carb cleaner. I sprayed ALL around the engine but it never changed idle even a bit. Used up almost a whole can. If it's a vacuum leak I can't find it. It's almost like the throttle cable is getting stuck when I let off it but it only happens when I'm in motion. That doesn't seem to make sense to me. Any ideas?
vengeancecube
03-16-2009, 05:18 PM
UPDATE:
Just for kicks I tried disconnecting the TPS sensor entirely. Lo and behold the thing worked perfectly. It idled a little low and would stall on occasion. Also I could detect the faint smell of gas. BUT when I drove, it acted exactly as it was supposed to. When I pushed the clutch and let off the gas, there was an immediate drop in RPM's.
Knowing this I the TPS voltage when connected. It was reading 0.99 volts. Adjusting it was a bit of a project as I had to remove the IAC to get access to the screws which of course meant I had to remove the throttle body to gain access to the IAC bolts but I got it all set. I wasn't able to adjust the TPS much. I got it down as far as I could go (0.94V). I also took the opportunity to clean out the IAC and Throttle Body with some carb cleaner. Both were surprisingly clean. The IAC looked like it may have been recently replaced. When I got everything back where it was supposed to go, the car started right up. It now idles at about 700 RPMs. BUT the surging problem still exists when I'm driving. And still only when I'm moving. Exactly as before. The effect has not diminished at all. Could it be that I need to replace the TPS entirely? Or is it likely that the problem is elsewhere and it's coincidence that it goes away when I disconnect the TPS?
Just for kicks I tried disconnecting the TPS sensor entirely. Lo and behold the thing worked perfectly. It idled a little low and would stall on occasion. Also I could detect the faint smell of gas. BUT when I drove, it acted exactly as it was supposed to. When I pushed the clutch and let off the gas, there was an immediate drop in RPM's.
Knowing this I the TPS voltage when connected. It was reading 0.99 volts. Adjusting it was a bit of a project as I had to remove the IAC to get access to the screws which of course meant I had to remove the throttle body to gain access to the IAC bolts but I got it all set. I wasn't able to adjust the TPS much. I got it down as far as I could go (0.94V). I also took the opportunity to clean out the IAC and Throttle Body with some carb cleaner. Both were surprisingly clean. The IAC looked like it may have been recently replaced. When I got everything back where it was supposed to go, the car started right up. It now idles at about 700 RPMs. BUT the surging problem still exists when I'm driving. And still only when I'm moving. Exactly as before. The effect has not diminished at all. Could it be that I need to replace the TPS entirely? Or is it likely that the problem is elsewhere and it's coincidence that it goes away when I disconnect the TPS?
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