The Truck- 1996 Blazer 4wd with the 4.3 and automatic transmission. 118k miles. I have recently changed the spark plugs, wires, cap and rotor, and all vacuum lines. The original lines were beyond brittle, and had cracked to the point of having holes in them.

The Problem- Driving up to speed, under different throttle positions, perfect. From about 50mph up, when just holding speed on flat ground the truck surges, and it can be seen on the tach. Under acceleration (or up a hill) from any speed there is no surging.

Through the search button, I found this thread. https://blazerforum.com/m_90272/tm.htm

Is the solenoid being talked about also referred to as the "Transmission Control Solenoid?"

http://www.autozone.com/N,11200623//...eResultSet.htm
Autozone PN 52-0203

Thanks
It was the most informative of any I have found. I have not founda post that solved this problem.

 

Have you recently cleaned your MAF sensor? I was having a very similar problem with mine... surging at highway speeds but not under acceleration. While changing the waterpump I cleaned the MAF sensor with some CRC MAF sensor cleaner. I was amazed at the difference. The truck now runs great... no more annoying surge!

 

Thomas,

First of all welcome to the Blazer Forum.

Couple of questions, do you have an SES light displayed? Do you have any codes? if so what are they?
What you describe sounds alot like what I had been dealing with until I got a SES light, and then THE DREADED PO300 code. Hopefully your situation isn't that bad, but you may want to look at that post. (start on page 2 and look for the summary if you don't want to read the whole thing) maybe there is something in it that can help you.

Gator

 

I would suggest also cleaning the EGR and changing the fuel filter.