Bad IAC on 95 GT?

stangman281v8 · Oct 24, 2016

My 95 GT will sometimes die right after start up, the CEL comes off and on intermediately, and the car will sometimes hesitate under load. The car also sounds like it has a cam at idle. I have changed the plugs, wires, cap/rotor, EGR valve, Cleaned MAF, and fixed vacuum leaks. Could it be IAC?

07GtS197 · Oct 24, 2016

Sounds like the fuel pump to me. Especially when you say itll start and immediately stall. The fuel lines will be pressurized but once that pressure drops when the car starts the car will die. Get a fuel pressure gauge on it to verify a bad fuel pump before replacing it.

GearGambler · Oct 27, 2016

I doubt it being the IAC. I would say a vac leak, and I know you already fixed it, but sometimes there's more than one. The CEL coming on means that there will be a code. would you please pull the codes and let us know what they are?

stangman281v8 · Nov 1, 2016

I had an IAC on the shelf and installed it with no luck fixing the issue. I double checked the vacuum lines, and I am pretty sure I fixed the ones that were faulty. The code is a PO172 and comes on intermediately. I will fire the car up, give it some gas, and the RPMs drop off and the car will die. I will start it again, and it will run. The car does act like it has a cam in it with the rough idle. I will check fuel pressure next. Any suggestions?

GearGambler · Nov 2, 2016

I would say to do a base idle reset next. Is there an aftermarket throttle body installed?

Pull the spout, unplug the IAC and the TPS. Start it up, Set the base idle with the idle screw on the TB. Shut the car down, plug everything back in, start it up again and see if it's better. It must be at operating temp when you do this in order to get a stable idle.

Checking the fuel pressure is always a good idea. One thing to check is to pull the vac tube off of the fuel pressure regulator and make sure you dont smell or see any fuel. if the diaphram goes bad, it will suck fuel right into the intake.

stangman281v8 · Nov 13, 2016

Sorry for the delay. I just moved the car into my friends shop for the winter. While triple checking everything, I noticed that the one vacuum line that feeds on the underside of the upper intake manifold was dry rotted. I decided to pull the upper intake manifold, and found that the second vacuum line that tees off into the upper intake manifold was completely broken off.

Since I have everything apart, I am cleaning and painting parts while until the gaskets come in later this week. If this doesn't change anything, I will check fuel pressure and reset the idle. I will keep this thread updated soon.

ttocs · Nov 13, 2016

try turning the key on/off/on a couple of times before you start it to be sure the line is primed to test the fuel pump. Could just be a leak in the line, even the S-line in the tank that would not even show a fuel leak on the ground.

stangman281v8 · Dec 19, 2016

Update: I did a fuel pressure test, and it is showing 12 PSI at the fuel rail. I am going to change out the fuel pressure regulator tomorrow. If this doesn't work, I will get a new fuel pump coming.

stangman281v8 · Jan 2, 2017

I changed the FPR with no change on how the car is running. I changed the fuel pump tonight. I am showing good pressure at the rail, but the car still runs rough and doesn't really have throttle response. The car will start and die, then run rough. Biggest thing is no throttle response.

Any suggestions to look at next?

stangman281v8 · Jan 24, 2017

Update: I pulled the intake manifold off, cleaned the injectors, replaced PCV, and TPS sensor. The car runs great and I believe the issue has been resolved. Thanks for everyone's help.