When I start up my car ('87 Iroc TPI) it starts idling real rough, almost like I have a hot cam. And during this rough idling, looking at the tach, the needle quickly goes up then down repeatedly for a few seconds, like its surging. Coincidently, it does the same thing when I put the car in overdrive on the highway. All the sudden it starts running real rough. It doesn't do it in town since I'm not in the overdrive gear. Could this be a sensor thing? When I first got my car a few years ago it pretty much did the same thing. If I remember correctly, they put in a knock sensor or something. Also why does it seem not to run rough in town. When I'm at a stop light it runs good and acceleration seems normal. I'm going to try to fix this myself with you guys help. Thanks.

 

*bump

 

yeah i have been trying to tackle this EXACt problem for a little while now.....havent actually fixed it yet......here are some things i have been told might be the problem:
--vacuum leak (most likely this)
--IAC
--O2 sensor
--ignition

so far i have changed a bunch of vacuum lines, changed the o2 sensor, cleaned the IAC....thought it was done, but it came back!

this weekened i plan to replace cap/rotor and wires

i hope one of us figures it out! best of luck

 

Oh yeah. I am in the same boat as you. Although I do believe I have found it in mine. In my car it seems to be distributor/rotor ignition system related. So I would check that. Check your timing and your vacum hoses. Make sure your IAC system is clean and just to be safe check your air filter or intake for obstructions. Also make sure all the sensors going to your injection system are plugged in and working. Mine was real bad. I had issues in all the above areas. Almost all of which are worked out now.

 

What are the most important sensors that might be the cause of the problem? Thanks