I have a 99 4wd 4dr and just recently started surging symptom, it has done it to me twice, once the other day while climbing a large straight ridge near my home. I had the cruise set at 60 and it was like it couldn't maintain without surging real hard letting off and then accelerating again it did this all the way up the hill. I run this road almost every day to work and it was definately not normal. Today on my way into work started doing it again, this time the cruise was not on and I was only traveling at 35 down a long straight for about a mile. Before this started happening I have been noticing that down the same large hill in cruise, sometimes it will stay at 60 all the way down the hill with no problems and other times it will not even attempt to slow the vehicle down and by the bottom of the hill I could be doing 75 or better if I didn't hit the brakes. I should also mention that the cruise has no problem mainting speed in the flatter areas. I also have some idle issues where it will idle high after shifting from any gear into park, than after an abnormal amount of time it will come back down to normal.

The catalytic converter has been rattling internally for the past few months so was wondering if that could be causing some flow issues. I also just recently removed my cold air setup from spectre, because I though it was causing a some of the other problems. I've cleaned the MAF, but am not sure how to get at the EGR. I intend on cleaning the IAC tonight. I've read several other threads and it sounds like it could be the TPS, FPR, Fuel pump, 02 sensors and several other things. I broke the small plastic cage off the tip of my Intake air charge temp sensor and was wondering if maybe that had anything to do with it. I also read how to test the TPS from Swartkk, he says to stick the probes in the back of the plug going to the TPS but I found it impossible to do with the intake on so I was wondering if there was an easier acess point, or if you could just read a changing resistance because I believe that all the TPS is, is just a Potentiometer.

I was wondering if you guys could help me narrow it down. I don't have a code reader but I have yet to recieve a check engine light. Thanks for any help.

 

Check engine light on? Any stored codes?

When was the last time a tune up was performed (plugs, wires, cap, & rotor)? Have you cleaned the EGR valve and MAF sensor?

What were the weather conditions (hot, humid, cold, dry, etc) when it did this and does it seem to happen during a certain type of weather?

As far as the TPS goes, you can measure the resistance. I do not have the values handy, but I may have posted them in the past. I have two back probes for my mutlimeter that makes it easy to do this task, but not every mutlimeter comes with detachable tips.

I doubt you did much damage to the IAT sensor, but it really is not that expensive to replace. It should not cause a random issue though... If you had a compatible scan tool, you could monitor the IAT values while you experience the issue.

 

No CEL, I don't have a code reader but I will see if I can get my hands on one this weekend.

Weather was cool (60F) and dry low humidity both days.

I did clean the MAF, were exactly is the EGR on this vehicle? I see the piping for it where it plumbs into the intake manifold. I bought this vehicle a year ago, the dealership that I bought it from did all the previous maintenance and had proof to show it to me. I'm not exactly sure when they did plugs, rotor, etc. though maybe I'll give them a call. It has 148,000 miles so it maybe time for that stuff again.

I find it had to believe that spark plugs and rotor would cause the run away issues with the cruise though.

 

You definitely have a combination of issues. A dirty throttle body or sticking throttle cable can cause the runaway condition.

EGR valve is located on the front of the intake between the A/C compressor and the alternator. It is about the size of a soda can.