Hi All, not new to Mustangs and have had many in the past, but picked up a 1998 Cobra this past spring after not having a Mustang for probably 6-7 years. Car is in really nice overall shape, but I have been plagued with a high idle issue since I got the car.
Issue #1 -> Car starts, runs and drives fine, but has a high idle after driving the car for some time. When I say high idle I mean the car won't go below 1,000rpm at idle and after cruising for a bit the car will idle at 16-1800rpm. Often times the car will start and idle fine and the only way to get it to return back to acceptable idle is to shut car off and on again.
The car has zero emissions parts on the car. No smog pump in passenger fender, no purge valve and no EGR valve. It was like this when I got it. I was told these parts were removed because the car got a CEL for emissions related issues and the previous owner had everything removed and a tune put on the car by STL Mustangs in St. Louis.
Thinks I've tried so far to fix the issue:
-Replaced IAC with a brand new Hitachi IAC - didn't do anything. If not make things worse.
-Cleaned and checked MAF, TB
-replaced broken TPS sensor connector on the engine harness side
-unplugged MAF entirely and drove car around. No difference at all with MAF unplugged.
-smoke tested the car using an automotive smoke tester borrowed from a mechanic buddy of mine looking for vacuum leaks. Had a tough time completely sealing the intake tube, but had a tiny bit coming out of the tester seal there and a small amount coming from the little cup on top of the iac. My understanding is that it's normal to have some coming out of the iac?
-set base idle on the car meaning unplugged battery, unplugged IAC, let car sit for 20 mins, plugged battery back in, set idle to 600rpm at throttle body screw and verified TPS voltage at .88-.90. As soon as I plug IAC back in it wants to shoot the RPM right back up. If I unplug TPS the car will idle fine.
-Flashed car with an SCT X4 to whatever their canned tune is to try and help eliminate any tune issues. If anything this made the issue worse as well. One thing I did notice when doing this is the SCT could see that the car already had existing changes to the ECU for the removal of the emissions parts. I have a "Theft" light that flashes due to this (I believe).
I think that's it. I am also getting several codes on the SCT X4:
P0122 -> Throttle Pedal Position Sensor/Switch (TPS) A Circuit Low Input -> Had a busted TPS connector and replaced it with a new connector
P1516 -> Intake Manifold Runner Control Input Error Bank 1 -> Not entirely sure what the deal is here. Both sides spring open and closed fine and previous owner says that nothing with the IMRC's was ever messed with
P0443 -> EVAP Purge Control Circuit -> Purge valve is gone entirely
P1445 -> Purge Flow Sensor Circuit High Condition -> Same as above
P1519 -> Intake Manifold Runner Control Stuck Closed -> This is the other IMRC related code.
One other thing I also find very interesting is that the LTFT's on the car at idle are very high. Logically this would tell me that there is unmetered air entering the engine somewhere and the ecu is trying to add fuel to correct for the lean condition, but I don't see any visible vacuum leaks via the smoke test.
Any ideas? Things to check before I go and drop this thing off to Lee Blankenship?
Issue #1 -> Car starts, runs and drives fine, but has a high idle after driving the car for some time. When I say high idle I mean the car won't go below 1,000rpm at idle and after cruising for a bit the car will idle at 16-1800rpm. Often times the car will start and idle fine and the only way to get it to return back to acceptable idle is to shut car off and on again.
The car has zero emissions parts on the car. No smog pump in passenger fender, no purge valve and no EGR valve. It was like this when I got it. I was told these parts were removed because the car got a CEL for emissions related issues and the previous owner had everything removed and a tune put on the car by STL Mustangs in St. Louis.
Thinks I've tried so far to fix the issue:
-Replaced IAC with a brand new Hitachi IAC - didn't do anything. If not make things worse.
-Cleaned and checked MAF, TB
-replaced broken TPS sensor connector on the engine harness side
-unplugged MAF entirely and drove car around. No difference at all with MAF unplugged.
-smoke tested the car using an automotive smoke tester borrowed from a mechanic buddy of mine looking for vacuum leaks. Had a tough time completely sealing the intake tube, but had a tiny bit coming out of the tester seal there and a small amount coming from the little cup on top of the iac. My understanding is that it's normal to have some coming out of the iac?
-set base idle on the car meaning unplugged battery, unplugged IAC, let car sit for 20 mins, plugged battery back in, set idle to 600rpm at throttle body screw and verified TPS voltage at .88-.90. As soon as I plug IAC back in it wants to shoot the RPM right back up. If I unplug TPS the car will idle fine.
-Flashed car with an SCT X4 to whatever their canned tune is to try and help eliminate any tune issues. If anything this made the issue worse as well. One thing I did notice when doing this is the SCT could see that the car already had existing changes to the ECU for the removal of the emissions parts. I have a "Theft" light that flashes due to this (I believe).
I think that's it. I am also getting several codes on the SCT X4:
P0122 -> Throttle Pedal Position Sensor/Switch (TPS) A Circuit Low Input -> Had a busted TPS connector and replaced it with a new connector
P1516 -> Intake Manifold Runner Control Input Error Bank 1 -> Not entirely sure what the deal is here. Both sides spring open and closed fine and previous owner says that nothing with the IMRC's was ever messed with
P0443 -> EVAP Purge Control Circuit -> Purge valve is gone entirely
P1445 -> Purge Flow Sensor Circuit High Condition -> Same as above
P1519 -> Intake Manifold Runner Control Stuck Closed -> This is the other IMRC related code.
One other thing I also find very interesting is that the LTFT's on the car at idle are very high. Logically this would tell me that there is unmetered air entering the engine somewhere and the ecu is trying to add fuel to correct for the lean condition, but I don't see any visible vacuum leaks via the smoke test.
Any ideas? Things to check before I go and drop this thing off to Lee Blankenship?
