Astro van.

[SCUMFROG]

I have a 1999 Chevy Astro van all wheel drive with a 4.3 v6. When I'm going down the hwy it hiccups at speed. It feels like I'm hitting a puddle, you know how your car slows for a second when you hit one. Engine light is not on. What could this be… Other wise it runs fine.

[Jeremy airjer W]

Does it do it consistantly at a particular speed?

Do you notice a loss in acceleration occasionally?

Do you ever hear a hollow rattle from under the vehicle?

How many miles are on the vehicle?

Have you ever noticed if it is worse when its damp or cold out?

[SCUMFROG]

All of the above.

not really a loss in acceleration, but it does feel like it doesn't have the umph it used to.

I've only felt it on the hwy.

The rattle I think is the exhust.

[Jeremy airjer W]

Alright heres some things to check into. Bad plug wires. If there arcing everyoince and a while you would notice a "hicup" and no check engine light. Broken up catalytic converter, may or may not see a check engine light. Pluged fuel filter. A MAF going bad, I've seen plenty of these go bad with no check engine light. Least likely but still plausible TPS sensor.

Do you ever notice that the RPMs go up like the trans is shifting out of overdrive?

last question is it just a quick jerk lasting a split second or does it feel like it takes a couple seconds to remmedy itself?

[SCUMFROG]

The rpms don't change that I notice. I have had that rattle for a while and it is gett worrse. I'll look at that frist. Fuel filter is new about a year ago. Plug wires are about 3 years old. I was thinking the TPS. But someone told me the light would come on. How can I check the MAF?

[Jeremy airjer W]

One thing you can try is unplug the MAF sensor. This may or may not work on a 99 but it did help in figuring out what was going on in some older grand ams. If it does work it sjhould start and idle fine. It will flag the check engine light!! Drive it and see if there is an improvement in performance. Abviously a person with drivablitity experience would know what to expect with it unplugged so you may or may not feel a difference. If it doesn't want to idle or if it doesn't want to run right at all please do not temped fait and drive it.

Reading the MAF signal with a scan tool would be the better way to go but without one your kind of out of luck. Give it a try and see what you think!

The more I think about it the more I would bet it is a maf problem. You may want to pull it off the air snorkel just to see if there is a lot of debris built up on the screen. I have seen that a couple of times. I would not reccommend replacing it out of the blue!! It can be an expensive item!!!!

[jt24]

How about changing fuel filter? Thats where i would start.

[SCUMFROG]

I'm thinking it's electrical. Last night after it has been raining for a while. I was at the store and when I started it run fine but my head lights were a little dim and the volts were down under 14 on the gauge, 14 is normal. As I drove it home the volts came back up This morning it was fine. I'm going to take it in and have them check the electric out for me.

[theoilman]

I have a 96 Astro that has had egr valve problems repeatedly, and other mechanics have told me it was a troublesome valve design. It sometimes sets an engine code, but frequently doesn't.

Also, 3 years is the longest I have ever gotten from plug wires.

[SCUMFROG]

I'm thinking its the wires also. It hasn't been it for 3 days now. I'll get them replaced and go from there.

[Jeremy airjer W]

Before you change them spray them down with soapy water and see if you can see them arcing. This can also be usefull if the coil or cap is leaking.

[SCUMFROG]

I can't see that far back.. Dang van.. To much stuff in the way..

[fishhook8]

I have owned two general motors vans 4.3 liter. They are notorious for bad fuel pumps. Changed them on both vehicles a couple times. The last major issue I had was the engine would turn over but not fire. It took several trips and many months to find out that it was the fuel pump relay. A $17 part. It happened when coming home the vehicle would not start, eventually It started. I called the Chevy garage saying I was coming in and was not shutting my vehicle off until they hooked it up to the computer. It told them it was the relay. If I had shut off the engine the warning light would have cleared. I know the frustration.

[SCUMFROG]

I just replaced that in the fall. Not cheap to replace it. It was in the gas tank.