Hi,
I have a 86 iroc z28 and when I first get in it after letting it warm up, I will put it in DRIVE and wont even touch the throttle and the car will go all the way up to 20 mph and then once there it will Rev up to 1500 rpms and then back down again to 500 rpms and does it like that 4 times in a roll and then it stay at 20 mph.....what could this be?

The tranny is a 700r4

I appreciate any help I can get:/

 

Does that happen everytime you start the car or just when it's cold? What happens if you start it and just let it idle?

 

It does this everytime...when I start it and just let it idle, it idles normal.

 

Surging is usually caused by lean AFR. Could also be an IAC valve or control circuit problem.

 

Is that a spendthrift fix?

 

Spendy fix* sorry.

 

I never said that any one issue is causing your symptom. Therefore, to say it is a spendy or a cheap fix is premature. Before you jump at any solution you really need to pinpoint to the cause of the problem. As I said, most surging is caused by lean AFR. Lean AFR at idle is most often caused by unmetered air, or in other words, a vacuum leak. Aside from a failed manifold gasket, vacuum leaks are generally a cheap fix. Lean cold idle can also be caused by a coolant temp sensor that's scewed to the hot side, causing the ECM to lean out fuel while the engine is still cold. To check these things, you really want a scan tool to monitor data from the ECM, both while the symptom is present and while it's not. On datastream, you can see all of these data pids along with Integrator and Block learn, which are your short term and long term fuel trims. Fuel trims tell you whether the engine is being over fueled or under fueled. Fuel trims and O2 sensor voltage can tell you if the O2 sensor might be faulty and causing the ECM to lean fuel when it shouldn't.

 

There is a guy on youtibe with the same problem, it turns out he had a faulty coolant temp sensor, so with that being said, I am still gonna make sure it's not anything else by taking my car up to a mechanic and having them scan just to make sure.

Thank you for your time and effort