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Surging/Bucking around 45MPH Low RPM

20K views 22 replies 10 participants last post by  Ravalli Surfer 
#1 ·
Hello

I have a 2004 Trailblazer EXT 4.2L that has a surging issue that starts around 45MPH at Low throttle. The car feels like it is searching for a gear, missing revving up and down. I know it is locking up because you can lightly tap the brake and the RPM jumps up a couple hundred and then it stocks bucking on me.

I just had the transmission fully rebuilt last week, And it was doing this prior to realizing there was any issues with the transmission.

I read somewhere something about the TPS can get a burned spot in it which can cause a similar issue but I need advice.
 
#2 · (Edited)
This week I have replaced a few parts with no change such as Front o2 sensor, and Throttle Body.

ANY thoughts here? Seems like a transmission rebuild would have fixed this unless something did not go as planned with the build.

I also went back to the Transmission shop and they are going to take a look at it next week.

in my original thread it should have said "And it WAS NOT doing this prior to realizing there was any issues with the transmission"
 
#3 ·
2004 Trailblazer 4.2

I've been having the same problem. My battery went dead on me and when I jumped it it was shutting off with defrost on. And when driving 45 mph down the road the idle would fluctuate and act as if it was going to die. I Cleaned the throttle body. When taking the connector off the black tab broke. Now most of the time it idles fine with defrost on but every once in a while the idle start jumping up and down. When driving 55 mph the rpm fluctuates a little bit. If I get going 60-65 it starts fluctuating 200-300 rpm. It did not do this before. Check engine light is on but the only code it is reading is a temp code which has been on since 2 yrs ago when I bought it. I've always been told that I don't need to worry about that code.
Do I need to replace the throttle body?
 
#9 · (Edited)
Post was meant for LMMJ. Hense the post quote. A FYI though.

The radiator and transmission cooler are one unit separated by a wall. If you have an unexplained loss of ATF with no visual leaks then that wall may have a pinhole between the two cavities. It starts with the slow loss of AFT because of the pressure differential between the transmission and engine cooling systems during operation.
 
#11 ·
Well took the Blazer back to the transmision shop that rebuilt it and they said the TCC soleniod was working according to thier scanner and nothing esle pulls up on any scanner so this is a mystery. But i call bull crap on them. no engine lights and nothing pulling up on the scanner.

This week ill be replacing the TCC solenoid simply because during surging when I tap the pedal lightly it stops surging as soon as i let off it continues.

Ive replaced at minimum with no change and at great expense the following

Throttle body
Spark Plugs
Air filter "K$N"
AIT sensor
Both 02 sensors
All 6 Coil Over Packs
Fuel rail pressure Sensor
 
#16 ·
I am having the same problem my transmission was rebuild 4 times and they can't figure out what's going on. They want to put a bigger transmission cooler on it. I doubt this will fix the problem. I want them to put a whole new transmission in it since they had rebuitit 4 times and have kept my truck for over 30 days. They have replace. cam shaft sensor, cam shaft actuator, 02 sensor fuel filter, plug and wires and cleaned the throttle body.
 
#23 ·
FWIW, I had the same symptom for a couple years and replacing the MAP sensor appears to have fixed it. I read somewhere that a bad MAP can cause the computer to send faulty data to the transmission, causing the surges
What you say is (mebbee) true and I admire your spunk in saying it ... put a foot in and go --- right?

Anyway ... you are responding to a zombie post and we tend to get all wrinkled up here when people drag up these DBs and re-energize them.

It would be a lot better to make your observation in a fresh post with a sexy headline --- like:

A Semi-naked Woman Told Me This Is My Problem --- (etc)

See?

Me? ---> I just give some silly suggestions here and I really don't know what I'm saying most of the time.
 
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