Stang Bang98

Hi. Im somewhat new to this site, hope im not reposting, but i didnt see anyone with my "exact" problem. First off, the hurt pony we're talking about is a 1998 GT. 4.6L, AUTO, SOHC. The only upgrades to the vehicle at this point include a BBK cold air intake with a K&N filter, and a American Thunder Flowmaster exhaust with 40 series mufflers. Now, the problem is something ive just now picked up on, not sure if its been there long or not, but appears to be getting worse. When it rains...or its cold....or even chilly outside...I have a hard time getting it to start. it tries to turn but no fire. If it does start under these conditions, it usually stalls out in the first 2 or 3 minutes of idling. After i finally get it running, sometimes it actually stalls while driving it...at any speed. It happens pulling out of the driveway at 5 miles an hour, or on the interstate at 75 miles an hour (...not good.) Somedays (usually warm outside) it starts up fine, and theres no stalling at all. Thats only half my struggle. The other problem is that....(choosing words carefully...) during a constant acelaration of the same speed, the car seems to have a hard time determining what gear it should be in. its kind of like a miss i guess. this problem continues until i press the gas down, or i let up (allowing the car to be certain of correct gear). I havent noticed a trend in what RPM or speed the car is at when this happens, but instead of smooth shifts, it acts confused. When the car is in park or at a stop light, the idle is a low 600, and in turn shakes the car like its on its death bed. I know that on the 98s' the idle speed is non adjustable. So far i have gotten new spark plugs (set gap appropriatly), checked wires (there ok), checked for vacuum leaks, sprayed throttle body cleaner, checked IAC, and im sure a few other things that are slipping my mind. Please help, this is driving me crazy. Thanks.

grabbem88

tap that iac then see how it starts.my 98gt had a bad iac

dothack

+1

same, i clean it the first time and it last me about a month..i bought a new one and no probs with it ever since.

droptoppony

My guess would also be the IAC valve. I had to change mine at 75,000 miles...its an easy fix .

Poobs

Hmmmm ? Definetily check the IAC further

Also - The wires should not be shot yet, however checking them visually can be misleading. Best way to actually see bad wires is with the hood open at night when it is moist out.

The problem could be moisture related or temperature related. Only you can determine that.

Idea - keep the car in a garage for few days to see if it makes a diference, put an old blanket over the motor overnight to absorb the moisture ( engine must be cold ! )

Blow dry the wires and coils before starting

Stang Bang98

Hey i appreciate everybody being so helpful, and I am going to check that IAC valve. Im with you guys...i read in my hanes manual and it also says that this could be the problem. i'll try cleaning it first, and see what happens. im going to do all that on tuesday, and i'll let you guys know what happens. Hey droptoppony....my cars got 74,000 miles. Seems to be a pattern here. Thanks again guys!

Poobs

Good luck Let us know how it turns out.

Stang Bang98

Alright, i got a brand new IAC valve, no difference what so ever. Does anyone have any other suggestions. im desperate. thanks for helping.

Poobs

Ok you said that the check engine light is not on - right ? Maybe U should go to autozone and have them read anyway.

There are a few things you can check relatively easy that could be causing the problem of hard starting unsteady idle and cruising RPM.

I'll try to write them in order of what I think is their likelyhood.

Vacum leaks - with the motor at a steady RPM spray carb cleaner around the throtle body area, vacum hoses etc. The dile will change soon as you hit a leak area. Any hose or joint is a suspect including the rubber intake joints aft of the MAF.

TPS (Throtle Position Sensor ) . This can be checked with an ohmmeter. I'll try to find a link on how to do this. Basically it needs to read a certain amount of ohms resistance at idle and change incrementally as it is moved thru its range. It must return to the same reading as the throtle pedal is released and if the shaft it moved.

MAF Mass airflow sensor. This is a heated element in the intake air stream. Make sure it is fully in the air path. All I know to do with it is clean it carefully with alcohol or other solvent that does not leave a residue.

Air Temp Sensor. This is the other resistive heated type element in the intake air stream - clean
it too.

O2 sensors. These normally set off the codes and or check engine light. I'll try to find info on the basic workings of these and post the links.

II 98 GT II

If the check engine light isn't on, then it's a waste of gas to drive to autozone.