Chevy & GMC Vans

1998 Astro 4.3. When I first start it, hot or cold, it is real sluggish on acceleration for a few blocks. After that it seems to do just fine. It seems like a sensor is reacting to slow. I thought about the intake air temp sensor or possibly the throttle position sensor. I have already had to do the intake gaskets, wonderful coolant leak, it acted like this before the repair and I was hoping it would go away after doing the intake but it is still the same. Any ideas would be much appreciated. It runs and idles great other wise. There is no check engine light with this either.

Actually I was waiting to see if anyone else was going to post and add to that.Start out with knowing you have a sound foundation to work with first.Do a cold compression test on all cylinders and the same with a leakdown test.Read all the spark plugs.
After that post what you have found. :-k

When was the last tune-up done? Maybe the plugs are getting bad.

The van has 95000 miles on it, uses no oil, and when I repaired the intake coolant leak 2000 miles ago the spark plugs I took out looked very good. I did replace the plugs, cap and rotor.
I do not have the equipment to do the compression test, I'm not sure I would want to after replacing the plugs.

And when you had the dist out,how did you re-time this engine?. :-k

The reason behind a leakdown test is it will pin point the path for you to look harder at and it is worth it to pay someone to do that for you if you don't have the tools and equipment.Aside from a timing question,I have a question about still a vacuum leak on the intake that closes up once the engine reaches a certain temp.some of that comes under the last touched theory.Ya do know that you have to keep a open mind to all possibilities in order to figure this out.

When the van does this it is such a short time I don't think temp has any thing to do with it. It will even do it when the motor is hot. As for the timing, I marked every thing very closly. Reinstalled and the book says no timing adjustment needed. All the o-rings on the manifold were replaced. And I'm quite open to suggestions.

I dont have a van as new as yours, but, on the older TBI ones, there was a Flap accross the air intake that would close until it got warm, then it would open and redirect the air. Maybe you have something similar that is getting sticky and slow to open ??