My van is a 2000 Express 3500 with a 5.7 engine. It has about 115,000 miles on it. The problem I am having is that when first started it will fall flat if I give it too much throttle. It is worse the warmer it is outside. Otherwise it starts and runs fine with no missing, etc. There are no computer lights or codes. I have replaced the fuel filter and run some injector cleaner. I have also replace the air filter, spark plugs, intake air temp sensor and coolant temp sensor. Any ideas or suggestions as to what to try next would be greatly appreciated.
Thanks,
Keith

 

99 express 3500 with 5.7liter

had same .problem @ 100,000 miles: upon starting, felt like it was running on less than 8 cylinders (e.g. 7 cyl), & would accelerate roughly.
At 100.000 miles, described to GM mechanic, could not find any problems.
this was an intermittent problem at the time (intitially).

Problem continued, though about 160,000 miles, but got worse (really rough). GM found the problem: (IIRC) the MAF (mass air flow sensor) bad.
He said they go bad on vehicles with high mileage.

Have you checked your MAF?

ihth

 

It hasn't really been running "ruff" or missing. I haven't checked the MAF sensor. Is there a way to check it without replacing it? Did you ever get a computer code? I still have no codes.
I did just replace the distributor, cap, rotor, and wires but that make no difference.

 

Wow, that was it. I found a new MAF on ebay for $80 with free shipping. Slipped it in last night. It hasn't run like that for a long time. I hope I get better mileage now also. Still don't know why I never got a code. I had a Windstar that the MAF went out on and it gave a code. What a pain to diagnose. Hopefully this post helps out some others with the same problem.
Thanks for your help.