Surging in drive with brake on.

[rsr911]

Not sure if this is engine or tranny related. My '91 E350 van surges when in drive with the brake on like at a stoplight etc. The problem seems to be worst once warmed up. It also does this in reverse, which is particularily annoying as I have to back down a gravel driveway hill to leave my house. Also if I go from reverse to drive and give it light throttle the trans seems to slip/catch slip catch. Under medium for heavy throttle it seems just fine which seems to rule out a slipping TC or gear. Since it does it in reverse I suppose I can rule out first gear line pressure. Normal driving is just fine although I sure wish it would shift a little firmer. The tranny doesn't always kickdown as low as I think it should. Sometimes I feel it should drop another gear and it doesn't, this could be normal as I'm new to diesels. I did some checking under the hood, the lever that the accelerator cable attachs to has a dash pot of some sort in front of it but the lever is not touching it. I can pull the lever towards the front of the truck and make it just touch.

I ran a test tonight at a light, with my foot on the brake and the engine surging I lightly pressed the throttle and the problem went away, it was just loaded against the converter.

I had a 460 in a '77 pickup that had worn mounts, it would rev up in gear as it twisted on the mounts and therefore pulled on the throttle cable. Going to run into work in the morning with the doghouse off and watch the motor.

Any suggestions are welcome of course.

I have run blended fuel in the truck, installed a prefilter and new fuel lines and fuel filter. It does this both on blends and straight diesel. The trans level is topped off, maybe even a touch high. The past week or so the MPG seems to be down as well. It's got a fresh oil change and fresh air filter.

[rsr911]

Well it's not the mounts as the engine doesn't move much, certainly not more that I would expect even of a new truck.

I need to check the throttle return spring yet. Tonight I could barely make out the problem rolling down a gentle grade off the throttle at about 45mph. I could just make out the surging.

Anyone have any idea what this might be?

[Snotzalot]

1st sounds like bad accel cable. Lubricate with oil, all of the linkages etc of the IP.

[Snotzalot]

>The tranny doesn't always kickdown as low as I think it should. Sometimes I feel it should drop another gear and it doesn't, this could be normal as I'm new to diesels.

Several things, check your TPS (throttle position switch) quite often a bad TPS will give you your symptoms. Also, there is an electrical plug that goes into the passenger side of the trans. Remove the metal shield and remove the plug. (There is a small keeper in the plastic) Blow out any water that may be in the plug socket. Replace the plug and check for any drive symptoms. Also the plug that you pulled can be bad and needs replacing. Usually just a pull and replace of the plug will clear up and drive issues.

[rsr911]

Thanks, will try those suggestions in the morning.