95 Tahoe troubleshooting slight surging

[Allan Johnson]

Hey guys. Long time lurker here but I finally joined and this is my first post. I joined to buy a headlight harness from gmachinz but now I have a problem so I'm glad I'm a member now. I have a 95 2 door that I bought a year ago with 102k miles. It sat for a few years and I'm still trying to work the cobwebs out of it. I have a problem that when I am part throttle and under load it has a slight surge/hesitation. I can hear it in the exhaust and feel it. The tach shows it a little but like I said it is slight. Idle is smooth. I have already put plugs/wires, fuel filter, o2 sensor, and an ignition control module. I have a suspicion that it is a TPS sensor because that is what it is acting like. It feels like I am giving it gas then letting up ever so slightly over and over. Sometimes when I want it to down shift it seems like it doesn't know what I'm telling it with my right foot. I am planning on putting a sensor on today bc we are going on vacation for Labor Day and I don't want it to leave me stranded again. I just wanted to see what you guys thought it sounds like. Thank you in advance and I'm glad to be here.

 

[DerekTheGreat]

Welcome! I lurked for a long time too.

Get yeself a scanner. I bought a Snap On MT2500 but there are others. I like my brick and it has paid for itself years ago. That will allow you to see what the sensors are feeding back to the ECM and make a better judgement call on the TPS. Pay attention to what the 02 & MAP sensor are doing too, along with what the IAC is doing. IAC reacts to the TPS big time. Crappy TPS caused an erratic idle condition with my truck.

I think I had the same problem your truck had, only being a stickshift I would see that if I tried to hold the RPM at say 1,500, it would waiver slightly. Never saw IAC counts change but if the ECM was commanding it to run a bit richer and then lean it back out, it would do that to the idle. I put a different 02 sensor in and haven't noticed it since. I had replaced the 02 sensor already last year but I guess it was no good. Figures, aftermarket junk parts.

 

[95TXSilverado]

Welcome to the forum! You didn't mention that you replaced your distributor cap and rotor? I just replaced mine and id did make a difference on the idle and smoothness. If you haven't, give it a try.

 

[Allan Johnson]

Thanks guys. I'm 99 percent sure it isn't the o2 sensor bc the reason I replaced it is bc the guy who did my exhaust didn't put the sensor back in it. I had to carry it to another shop to find that out. Of course they didn't check anything else bc they thought well here is the problem. No o2 sensor at all. It did this same thing without an o2 at all. I may see if I can rent a scanner. I don't want to spend a lot of cash on the electronics bc I'm going to a carbed 383 this winter. I have also read that it could be an egr valve causing it. I'm going to disconnect it tonight and see if it smooths out. It is idling perfectly. Starts smoothly. Shifts smoothly. Just the oh so slight surging cruising at about 2k rpm. Thank you and I'll report back when I try a few things. I have to go give the bill to the exhaust shop and see if they are going to do the right thing. Mpgs were horrible with no o2 sensor and it did trigger a cel. The tech also said there was an egr code in there that he cleared also.

 

[Allan Johnson]

Welcome to the forum! You didn't mention that you replaced your distributor cap and rotor? I just replaced mine and id did make a difference on the idle and smoothness. If you haven't, give it a try.

I have not replaced the distributor cap but I will. I replaced the ignition control module.

 

[94burbk1500]

I have not replaced the distributor cap but I will. I replaced the ignition control module.

United Motor Products makes a nice kit for these with brass conductors, I put one on my truck and love it, it was cheap too!

 

[Markgyver]

Check your fuel pressure also.

Sent from my SM-G935V using Tapatalk

 

[jsfrmsj]

mine was doing the same before my distro completely crapped out on me.

 

[The Iron possum]

The TPS is not a replaceable sensor. It’s integral to the throttle body on a 95 (at least mine is). You can test it by disconnecting plug and then checking voltage between the gray (+) and black (-) terminals. With key turned to on (not started) should be about 5 volts. Reconnect plug (key off) and back probe the dark blue wire with + lead and put - lead to good ground. Turn on key ( not started) and should have about 0.6 volts. Operate throttle by handl while watching meter (analog meter works best). voltage should increase smoothly from closed to wide open with a max around 4.5 volts. If voltage jumps erratically, then it is likley the TPS. These are the test instructions from Haynes manual. I would be surprised if it is TPS on such a low mileage truck. Bad EGR will cause surging under load. Been there, fixed that- eventually.

 

[Allan Johnson]

The TPS is not a replaceable sensor. It’s integral to the throttle body on a 95 (at least mine is). You can test it by disconnecting plug and then checking voltage between the gray (+) and black (-) terminals. With key turned to on (not started) should be about 5 volts. Reconnect plug (key off) and back probe the dark blue wire with + lead and put - lead to good ground. Turn on key ( not started) and should have about 0.6 volts. Operate throttle by handl while watching meter (analog meter works best). voltage should increase smoothly from closed to wide open with a max around 4.5 volts. If voltage jumps erratically, then it is likley the TPS. These are the test instructions from Haynes manual. I would be surprised if it is TPS on such a low mileage truck. Bad EGR will cause surging under load. Been there, fixed that- eventually.

I looked at the TPS and it is replaceable on mine. 3 bolts and a plug. I removed the egr vacuum line and plugged it with a nail. It definitely helped a lot but it is still doing it a little. I think the egr is stuck a little bit. I'm going to take it off and clean it this weekend while we are at the campground. I will check the TPS voltage while I'm at it. Picking up a distributor cap this evening. It's easy and cheap and probably needs it anyway. Pretty sure the entire problem is the egr junk. I can't wait until I get rid of all the electronic and emissions junk. It may be next year before I have the funds for the 383/4l60 (not E). If I can't get the egr valve cleaned and working properly I may break down and buy one. As soon as I get time to fiddle with it some more I'll update with the results. I just hope it makes it to Gatlinburg tomorrow. Last year it left us stranded at the campground and I had to get a taxi to deliver the parts to fix it. That's when the ignition control module went out. Thanks for everything guys.