This van runs great when first started and continues to run fine until it’s turned off and restarted. When first started vacuum at idle is steady at 21” and 10” at 55mph cruising speed. After parking for 10 to 20 minutes and restarting idle is still steady at 21” vacuum but the van hesitates on acceleration and runs rough at cruise with a 5” vacuum. If I continue to drive I get low vacuum trouble codes for the MAP and Oxygen sensors. I’ve replaced the oxygen sensor and performed a diagnostic on the MAP sensor which checks out ok. I’ve checked for vacuum leaks – none found. Does anyone have a suggestion on what to look at next?

 

Could the fuel filter be partially clogged? Also, check all your spark plugs and under the dizzy cap for corrosion. Might be related.

 

Spark plugs, cap and rotor have all been replaced. Didn't consider replacing the fuel filter because it runs so well when first started and driven. I've driven it up to an hour and it runs fine. It's just when I go back later in the day that it consistantly runs rough.

 

I just noticed its the tbi. You could try swapping the two injectors. They are the same and maybe the idle main injector is partly plugged.....when its cold the cold injector could be compensating. If the fuel filter doesnt fix it you could have the injectors cleaned, but try swapping them first.
I have a 2002 so different injection system, but I had some bad gas that clogged my filter, and I had no secondary power....because of the fuel pressure was fine but not fuel volume.....it was weird. Anyway, hope that helps.

 

I'll try a new fuel filter, but the van runs great when first started and runs fine as it warms up. I can continue driving for an hour or so and it will continue to run fine. It's only when I shut it down and restart after 20 minutes or so that I have a rough running condition. I'm thinking the ECU/ECM is acting up, but when reading the trouble codes I always get the 12 code at the beginning and ending of the reading. I thought this meant the ECU/ECM was working properly.

 

Maybe a bad o2 sensor when its hot. Have you checked for codes?

 

On first start and running the van until the operating temperture is up to normal I do not get any codes. On second start the van runs rough and I get two trouble codes MAP sensor low vacuum (33) and O2 sensor lean (44). I've replaced the O2 sensor and performed diagnositics on the MAP sensor which check out ok. The next day when I start the van it runs fine with no codes until I do the second start.

 

It might be the lean issue that is the problem, not the o2 sensor. I'm back to thinking its a fuel problem. Did you swap the injectors?

 

If it was a lean condition I feel like the rough running and hesitation would start during the initial running of the van. But it always runs well on the first start and continues as it warms up. It continues to run well for as long as It's driven. The hesitation and rough running always begins after trying to drive it the second time.

 

Replaced fuel pump, now runs great!!!!!