I have a 2002 GMC (I know this is the chev forum but more traffic here) and about a month ago the throttle was stickey (Dirty TB) I replaced the air cleaner, cleaned the air flow sensor & cleaned the TB & IAC. Started perfect, no more sticky throddle.

Now comes the problem. When the truck is cold it starts perfect, shut it off and restart fine. Shut it off and restart 1hr or so later it cranks long & starts hard, but once it finally starts you can turn it off and she will fire right back up. Another thing I noticed is when it is cranking long you can let off the key and it seems to start right when you let off the starter.

Been trying to fix this with no codes except for the other day the service engine soon started flashing, from what I have read this is bad so I thought I would check see if it'* something I am overlooking.

What I have done after cleaning the TB but before the Service engine soon started flashing.

Replaced Air Flow Sensor (Thought I might have ruined it while cleaning)
Replaced Fuel Filter
Checked IAC Valve Ohm readings. 4.5 & 4.8 (Seems good?)
Reset computer

Not so funny thing is that it ran perfect with the exception of the sticky throttle, now not so much...

Any ideas of something that I am overlooking?

The flashing SES light is a misfire. I would start with the ignition system. sounds like it'* weak. Pull the plugs and replace. Replace the plug wires if they are old. Test the coils, they might be on the way out. Also have the fuel pressure tested. Pulling the plugs will tell you if it'* fuel or spark. Weak spark and the plugs will look blacker and dirty, low fuel pressure will be more white and powdery.

Dan,
I'll pull the plugs tonight and have a look see, probably wouldn't hurt to replace them anyway.

My only concern is throwing parts at it without knowing what'* wrong. I would think that if it was plugs/wires/ignition it would start bad all the time... not just when it'* warm but been sitting for about an hour...

A weak electrical system does not like getting hot. If you don't know how old the plugs and wires are, it'* worth changing them. The coils can be tested, there'* a test for that in the tech info section. Another test you can try is when it'* dark, use a spray bottle and mist the plug wires and coil with the engines is running. Turn off the lights and watch for blue flashing.

Ok here'* where I am at. Didn't make it to town to get spark plugs today but I did some troubleshooting based on Dan'* advice. Seems as though the #4 cylinder is not running. I pulled the plug on each coil pack while running and this one didn't make a difference in the idle, had good spark arc from coil pack to plug wire though. Pulled the plug and it was black, but not wet. I'm going to check the Tec. section and see how to go about testing for a plugged injector.

If I am chasing my tail please feel free to correct me.

Kory

A plugged injector would not make the plug black. Bad spark or poor air flow will. So, you either have a bad plug wire, or a bad plug. Also make sure that plug wire is not touching the O2 sensor wire.

The injector Ohm'* were ok. Just for kicks I switched the plug & wire from the #2 cyl. with the non running #4 and the problem didn't switch cylinders like I had hoped. I don't think the plug or wire are the problem or the #2 cyl. would have stopped running.

I'll be stoping by the parts store tomorrow for some new plugs & test the coils & plug wires while I'm switching them out. I think the Chevy dealer in town will read codes for free, maybe that will help narrow it down.

Thanks for the help, I'll let you know how it turns out.

Kory

Try a compression test. A misfire is caused by a few things, a bad ICM will be random misfire, a bad coil should, but not always have a misfire on 2 cylinders. A single cylinder is generally a bad wire or plug. A bad injector can also cause a misfire, changing the injectors around should cause the misfire to change cylinders. After that it'* a mechanical problem, a compression test might show this. But I've seen broken valve springs cause a misfire and not show up on a compression test. Only found this by removing the valve cover and visually inspect it.

Heck, the plug could have a small crack in it. That would explain it acting good cold and being a problem when hot.

How good was the spark from the coil? Dan found the standard MSD breakdown over time when he was running some and didn't have any problems idling etc, but when it was WOT and the RPMS were high the coils gave him a weak spark and issues. Swapped to a good set of stockers and no more problems.

Yep, I tested the coils and they all passed. The engine would idle and drive with no problems. But once I got over 2100 RPMs it would misfire. A new set of coils corrected the problem.