I have a rebuilt 420a with an auto trans in my 98 GS. The complete long block was redone and during the install, I decided to put on an Unorthodox Racing Underdrive pulley, OBX ceramic headers, high flow cat, and I already had a generic (Bomz I think) short ram intake, EGR block off plates, Ractive plug wires and a Pro 1 Exhaust. From the first start up, the car turned over but would not stay on. I finally got it to stay on and actually raise and lower in RPM's but as soon as I would let off the throttle, it would bog down and shut off. It seems like something is keeping the car from staying idle but I can't seem to figure out. The fuel pump is working so I doubt that is cause. I bled the air out of the fuel rail and that seemed to help a little but still won't idle. I checked all the vacuum lines and everything seemed right. I know there can be many things to cause this to happen but am in the process of trying to rule out the possibilities. My main question is: would a faulty MAP sensor cause the car to shut off right away or would it just act erratically? Or how about a loose connection at the power steering switch? these were a few of the possibilities that I saw. I'm going to try and test some stuff with my multimeter tomorrow like the IAC motor and MFI (ASD) relay and also try to check the fuel pressure. Any help or input from you guys would be greatly appreciated.

My bet is the IAC. Been there done that. I had the exact same problem down to giving it gas to keep it running. My bet is the IAC. Check the TPS also. Assuming you have one, your Haynes or Chiltons will tell you the correct numbers for those tests. If i remember right, .38 to .52 is good for the IAC even though every single one i have checked has read .53, even the one on my car right now. Good luck and let us know what you find.
Cameron

I had this issue a few years ago and it turned out to be a real simple fix. Not saying you have the same issue, but worth a shot.

I have a MP 60mm TB. On the TB, the idle set screw rests against a small metal post. One time that metal post came dislodged from the TB and fell off, so the throttle plate was at the full closed position. When this happened, the car would turn over and start but would stall out right away. All I did was fab up a new post and JB Weld it in place. No issue since.

Check to make sure your idle set screw assembly is intact and working properly.

If it is, than I agree with the above, and its probably a faulty IAC. IAC issues seem to be pretty common on 2G's.

Good luck!

Did you line up the timing marks correctly? even if it is half off, will ruin your ability to idle. Take a straight edge to it and not eye ball it.

check fuel pressure, iac valve, you can manually unscrew the sensor tip on the iac, i just did the 4.0l jeep throttle body and had idling problems and if the timing marks are off the valves are shot. and do you have a check engine light on? and if not check your connections for all sensor like crank position and cam position sensors and all other sensor ive forgotten to connect sensors back in before lol. good luck hope you find the issue.

So I finally got some time and switched out the IAC valve and there was no change in events. Changed out the map sensor and it started up right away! I didn't even need to give It gas. It idled very smooth but I could here a tapping sound from somewhere. I initially thought it was just the lifters but it would go away. Well, a little further inspection and I noticed my intake cam gear wobbling like crazy! Turns out it was damaged during shipping ( R&L carriers). So I am now in the process of tearing off the Power steering and timing belt cover. Sucks A$$! Anybody here ever run their motor without the timing cover? I don't plan on doing it, just curious. Thanks for all the help.

Lots of people do it without issue while others do it and run into trouble. Bullet just had his timing belt tear off at the Shoot Out causing damage to head components and he believes it may have been becuase he ran without a timing cover and something got caught in there.

I personally wouldnt recommend it, but it does look cooler.

That tapping sound you heard may or may not be related to the loose cam gear. If you say it went away when the motor heated up to operating temp, it may be because of an exhaust leak at the manifold. Pretty common issue, I have personally dealt with it more than once myself.

I wouldn't recommend it. My alternator belt died at 6500 rpms and shot into the timing belt. long story short, my engine was 8 valves and rockers, 1 intake camshaft and 2 pistons shy of running.

Originally posted by RoninEclipse2G
I wouldn't recommend it. My alternator belt died at 6500 rpms and shot into the timing belt. long story short, my engine was 8 valves and rockers, 1 intake camshaft and 2 pistons shy of running.

:eek oh shit! My belt alt belt looks a little iffy. Maybe I should change it!

Originally posted by RoninEclipse2G
I wouldn't recommend it. My alternator belt died at 6500 rpms and shot into the timing belt.

Bingo! After a bit of looking and research, it appears that this is what happened to the NA at the Shoot Out. The alternator belt jumped up into the timing belt (I don't have the upper cover on, I just use a bottom "race" cover for stuff on the track).

Got lucky by just losing 8 rockers and replacing 8 intake valves.