Alright. HELP. 95 convertible z28 with an LT1. And it's messing with my mind. I took the throttle body off in January to clean it and try and figure out a different problem I was having (ended up being a cracked spark plug insulator, unrelated) anyways I reinstalled it without replacing the gasket, I just used the old gasket and RTV. After that the car was hard to start, the idle would run up to 2000 Rpm's on startup and then settle to where it was supposed to be. But this would only happen sometimes.I replaced the gasket finally, didn't help. I replaced both the TPS and the IAC, it didn't really help. I replaced the pressure regulator and that solved the hard start. Starts right up now. But it idles high, but only sometimes. In fact I will put it in gear and it will shift hard causing the car to jump. This only happens every other start up, and will stop sometimes when I just restart the car. It doesent seem to matter if the engine is hot or cold. No check engine light. The car actually has started to accelerate itself, it actually shifted into second gear just letting it idle. I tested the tps and the voltages are in range. I can't find vacuum leaks. I don't understand what's going on, my fuel economy is horrible, it annoys me trying to drive and this car is driving me insane! And just today the car is waiting to upshift. It won't shift until very high Rpm's so I'll be just driving around doing 40 in second gear and it won't shift until 3.5-4 grand. I'm seriously stuck

 

I'm no expert, but could it possibly be the master cylinder? Or possibly a sensor gone wrong on the throttle body?

 

Master cylinder? As in the brake master cylinder?

 

Oh it's an automatic btw...

 

try to get it scanned for trouble codes.

 

I don't know where I can. I'm stationed in California so they have a law against the parts stores letting you use their scanners. Since mine is a 95 it has the jacked up port, what scanner can hook up to the port and read OBD 1&2. To have it scanned here is like 90$ so I might as well just buy the damn thing. What scanner brands are there?

 

you have a obd1 computer and a obd2 plugin, have to use a obd1 scanner,

 

Test your O2 sensors. If you have an exhaust leak they could be the cause of the high rev problem. Also look at your pcv valve. Also could be the cause. If you can test your fuel pressure aswell.

 

Oh and if the engine light isn't on there's no codes as the obd1 doesn't save the codes.

 

Alright the exhaust leak might be the cause. I replaced the pcv valve recently but will check all that. But I know there are some OBD sensors that read 1&2 and have compatible connectors