RPM Surges and drops 93 cruiser (1 Viewer)

[thetrentmeister]

So i have recently had this issue happen to me after going on the first trip with the truck i bought a few months ago. This is a 93 with 230k, 4.88s, on 35s. Not sure what other information will be relevant.

After a camping trip this past weekend I was coming back from the mountains and all was normal until down the mountain on level ground and i got to the highway and was driving at highway speeds. At 60pmh+ and under 3,000 rpms i begin to experience 100-200rpm surges after the rpms hit 3,000 it begins to surge -100 to -200rpms. Anything under 60mph I don't notice this issue. It doesn't sure when i am pressing the accelerator or going down hill.

I have also noticed that my transmission fluid is pretty high.

At 30 seconds in the video is a really good example of my issue.
Video link:

I am not sure if this next thing that happened to me today is related to what is going on with my rpm surge but anyways after driving it today for a good two hour test drive to pin point when the rpms issue was happening I got back to my house and turned around in my driveway but once i put it into reverse the truck died on me, I started it and then put it back into reverse and it died again. I started it again and revved the engine a little bit and then I put it into reverse and it didn't die that time.

Also some trail pictures for you guys to look at if you don't have an answer and are just here to browse.

 

[BILT4ME]

So i have recently had this issue happen to me after going on the first trip with the truck i bought a few months ago. This is a 93 with 230k, 4.88s, on 35s. Not sure what other information will be relevant.

After a camping trip this past weekend I was coming back from the mountains and all was normal until down the mountain on level ground and i got to the highway and was driving at highway speeds. At 60pmh+ and under 3,000 rpms i begin to experience 100-200rpm surges after the rpms hit 3,000 it begins to surge -100 to -200rpms. Anything under 60mph I don't notice this issue. It doesn't sure when i am pressing the accelerator or going down hill.

I have also noticed that my transmission fluid is pretty high.

At 30 seconds in the video is a really good example of my issue.
Video link:

I am not sure if this next thing that happened to me today is related to what is going on with my rpm surge but anyways after driving it today for a good two hour test drive to pin point when the rpms issue was happening I got back to my house and turned around in my driveway but once i put it into reverse the truck died on me, I started it and then put it back into reverse and it died again. I started it again and revved the engine a little bit and then I put it into reverse and it didn't die that time.

Also some trail pictures for you guys to look at if you don't have an answer and are just here to browse.
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Check for codes.

I'd guess an O2 sensor.

Also look for a crack in your intake hose.

 

[Railwelder93]

My 93 (Also 4.88 and 35s) surges a little under heavy load, like going up a big hill. Not bad enough to make the rpm needle jump around like that, but very similar. Not really sure what it is yet.

I put in new o2s recently and it still does it.

Might try the intake hose next, that’s a good idea.

Mine doesn’t do it that bad so I haven’t really tried hard to fix it yet, but I think it is a unregulated air, or transmission issue.

 

[thetrentmeister]

Check for codes.

I'd guess an O2 sensor.

Also look for a crack in your intake hose.

I just went out and checked my intake hose and that has no cracks that I can see.

I did a code check on the truck and got a 41 code which is a Throttle position (TP) sensor- circuit.

What does that mean?

 

[BILT4ME]

I just went out and checked my intake hose and that has no cracks that I can see.

I did a code check on the truck and got a 41 code which is a Throttle position (TP) sensor- circuit.

What does that mean?

That tells you you're getting a wonky reading from the Throttle Position Sensor (TPS).

Check the wiring and make sure it's not loose.

Get an FSM for your year and adjust it according to the instructions.

May require a throttle body cleaning.

 

[thetrentmeister]

That tells you you're getting a wonky reading from the Throttle Position Sensor (TPS).

Check the wiring and make sure it's not loose.

Get an FSM for your year and adjust it according to the instructions.

May require a throttle body cleaning.

Sounds good from the googling and such I have done would it be good idea to buy a new one and replace? Or would adjusting the TPS yield the same results? I will also look into cleaning the throttle body.

It does seem pretty hard to find a 93-94 FSM though most of the links I have found on mud are dead.

 

[BILT4ME]

Sounds good from the googling and such I have done would it be good idea to buy a new one and replace? Or would adjusting the TPS yield the same results? I will also look into cleaning the throttle body.

It does seem pretty hard to find a 93-94 FSM though most of the links I have found on mud are dead.

Do the clean and adjust before you throw the parts cannon at it.

If you request a manual here, someone can point you in the right direction. Someone will chime in.

 

[BILT4ME]

Ask and ye shall receive!!!!

1994 FSM, ATM, CR, CRIB, EWD, NCF, QTR, SSC -- DOWNLOAD HERE

Directly downloaded from TIS. Includes original individual PDFs as well as compiled PDFs I put together. 1994 FSM, ATM, CR, CRIB, EWD, NCF, QTR, SSC, Wire Harness Repair Manuals: Google Drive Link Enjoy

forum.ih8mud.com

 

[lumbee1]

Looks like a TPS. I've replaced mine twice. Once when the OEM died after 20 years and again when the chinese knockoff from rockauto died. Replaced with OEM at $94. Another check for TPS function is to watch the needle sitting idle in park. It should be 650rpms once warm and AC off. If it climbs above 800 or 1000 or jumps around, then replace it.

I have a 95 and the throttle position had to be set to 11% but I was able to pull OBD2 codes to set it.

 

[thetrentmeister]

Ask and ye shall receive!!!!

1994 FSM, ATM, CR, CRIB, EWD, NCF, QTR, SSC -- DOWNLOAD HERE

Directly downloaded from TIS. Includes original individual PDFs as well as compiled PDFs I put together. 1994 FSM, ATM, CR, CRIB, EWD, NCF, QTR, SSC, Wire Harness Repair Manuals: Google Drive Link Enjoy

forum.ih8mud.com

Awesome thanks man! I work in HVAC and I am slammed so hopefully i can take some time to get to this and clean it but seeing this after a long day is awesome.

Looks like a TPS. I've replaced mine twice. Once when the OEM died after 20 years and again when the chinese knockoff from rockauto died. Replaced with OEM at $94. Another check for TPS function is to watch the needle sitting idle in park. It should be 650rpms once warm and AC off. If it climbs above 800 or 1000 or jumps around, then replace it.

I have a 95 and the throttle position had to be set to 11% but I was able to pull OBD2 codes to set it.

Yeah i'm not sure if i want to buy one yet. I do want to buy a new accelerator cable since mine is junk so if cleaning the throttle body and trying to adjust the TPS doesn't work I might just order both at the same time.

 

[lumbee1]

Awesome thanks man! I work in HVAC and I am slammed so hopefully i can take some time to get to this and clean it but seeing this after a long day is awesome.



Yeah i'm not sure if i want to buy one yet. I do want to buy a new accelerator cable since mine is junk so if cleaning the throttle body and trying to adjust the TPS doesn't work I might just order both at the same time.

I thought a defective throttle cable resulted in a sticky inconsistent accelerator pedal travel.

When my TPS started to fail, my tach started jumping slightly. As the day progressed, the jumping started happening more often with higher swings. By the time I got home, the truck was revving to 2500 and 3000 all on its own and it was very difficult to slow it down and bring it to a stop.

 

[Marco Lau]

could be sign of a bad fuel pump...

 

[thetrentmeister]

I thought a defective throttle cable resulted in a sticky inconsistent accelerator pedal travel.

Correct it is a separate issue, i was just saying if i was gonna order a new TPS I might as well get the throttle cable as well.

could be sign of a bad fuel pump...

This could also be something that is going on. It is on the list of things to fix haha which is a long list.

 

[thetrentmeister]

I took the truck to a local shop here in Denver and this is what they came up with.

So this is their diagnosis with the problem I have been having and I am not sure what route to take.

"TEST DROVE VEHICLE AND NOTICED THE RPM CHANGE BETWEEN 2K-3K IS HAPPENING WHEN THE TRANSMISSION
SHIFTS FROM 3RD TO 4TH GEAR. IT IS DROPPING IN AND OUT 4TH GEAR. WITH THE ECT POWER BUTTON ENGAGED
IT HAPPENS AROUND 65 MPH BECAUSE THIS ALLOWS THE GEARS TO RUN LONGER BEFORE SHIFTING. WITH THE
ECT BUTTON DISENGAGED IT WILL HAPPEN AROUND 45MPH. THE RPM CHANGE IT TOO FAST TO BE ENGINE
RELATED. THE TRANSMISSION FLUID IS FULL AND BRAND NEW."

"Confirmed RPM fluctuation in 4th gear. Appears to be the torque converter lock up engaging and disengaging erratically. Manual
shift position still allows up shifts (L-2 2-3). D,2, and L lights inop. ("D" bulb is common to burn out and just need a bulb
replacement, not as common on other bulbs, need further diagnosis, may not be related to shift concern) Shifter feel not very
positive, worn mechanism in shift gate??. Check and adjust throttle cable (from transmission). Check timing and IDL contact after
TPS replacement. Adjust brake light switch in attempt to single out issue with erratic shifting, little to no change on test drive."

And you can see it on the attached PDF if anyone is interested. It seems like such a specific things that I can't find anything using google not sure if I should just drive under 55 until I can figure it out or if I just throw some more money at it while it is in the shop.

Any suggestions or help would be appreciated.

 

[thetrentmeister]

Thank you guys for all of the responses, it turns out Japanese Auto was able to find out what the problem was and then found some other problems along the way haha

The main issue causing RPM surges appears to have been the neutral safety switch not being fully plugged in that mixed with the transmission range sensor. One of the vacuum tubes was off and the EGR valve harness connectors are pretty rusted and needs to be replaced. They also found out that the engine wiring harness has lost its heat wrap so that needs to be addressed before any of the wires have been exposed if they haven't already.

So if anyone else is having an rpm surge similar to mine these would be the things to check.