I just did my 3.4 swap and after I got most of the early problems worked out it ran fine for a couple hundred miles but now when its cold it starts hard, won't idle. Sometimes I have to start it 4 or 5 times and you have to keep your foot on the gas. After a couple of minutes it idles on its own but the RPM jumps back and forth between 500 and 1500. Once it get warm it runs fine but the idle stays way to high, like 1500 RPM. Is this a choke issue or do I still have a problem with the 4.3 TBI ajustment. I never had to do anything other than get the vacuum lines correct. The TPS from the old 2.8 TBI bolted right onto the 4.3 TBI. The injectors and the TBI were completely rebuilt.

I know everyone is very busy this time of year. But please someone sound off on this. It's getting colder and colder everyday and more of a headache to get this started in the morning. I did check the mileage (13.8 mpg) and it's about mile per gallon better than the old 2.8 so whatever the problem is it only really effecting the start. It runs pretty darm good after it gets warm except for the higher Idle that is, it idles at about 1500 rpm wqhen it get warm and you can tell its to fast.

First off, there is no choke, so you can scratch that theory.

Tell us a bit more about your 3.4 swap. Was the engine rebuilt? Did you use the 2.8 TBI or a 4.3 TBI or a Holley, or some combination?

It was a 3.4 out of a 95 Firebird and it supposedlly had 70K on it but it was spotless inside, lifters and timing set looked brand new, water ports were spotless inside, no sludge of any kind anywhere. Me and the mechanic who helped helpd me put it in are about 99% sure they had put a remaned engine in that Firebird shortly before it was wrecked and no one ever told the salvage yard about it. The TBI was off a 89 Astro Van with a 4.3 we completly rebuilt it and all the sensors off the old 2.8 TBI mounted right on to it including the TPS. I sent the injectors to Accurate Injector Service ( http://www.accurateis.com/index.php ) and had them professionally cleaned and checked and they spray a perfect pattern. We did have to drill and tap a couple of holes to hold the bracket for the throttle cable but it fits perfectly. We also had the intake professionally bored to match the 4.3 TBI. Thanks Jim I appreciate your help, I hope this gives you a better Idea of what we've done to it.

I am no professional mechanic, however I would also check the output of the O2 sensor.. If the sensor thinks it is hot, or if the computer thinks it is already hot (possibly a temp switch/sensor) it will take the improper readings and try to get the engine to run until it does get hot and the readings are correct. I would also check to see if there is possibly a "cold start" injector that is or was supposed to be with the system.

I would also check to see if there is possibly a "cold start" injector that is or was supposed to be with the system.

Not on this engine.

Michael

Most computers will disregard input from the O2 sensor until the engine warms up, and run a pre-programmed map of fuel/air ratios. In fact, if the engine runs OK at startup and then starts running like crap when warm, that actually points at the O2 or other sensors.

Well one problem fixed and one to go. The hard start was the coolant temp sensor. I thought that the fast idle problem was related since they both started about the same time but the new sensor didn't fix that, it still idles way to fast even after it gets warm. Any Ideas?? I did change the O2 sensor even though I knew it probably wasn't the problem, it still had the old one from the 2.8 and that was at least 115,000 miles old. Could the TPS be going bad or a vacuum line problem?, there are not any obvious problems with the vacuum lines.

Sounds like you either have a vacuum leak or the EGR valve
is hung open a little.

EGR on an idling engine or cold engine will make it act just like that.