91 Camaro RS. Junkyard 350 from Caprice put in it. I bought it. I've changed plugs, wires, distributor and coil, fuel filter, new exhaust but not the y-pipe its cracked and I had them weld it. It didn't hold. New alternator and battery. Since I got the car I've been trying to fix this bug. It has some sort of electrical problem. I don't know..... It starts fine. It idle fine. But then sometimes my tach just starts going nuts 3500 - 4500 it reads up and down. But I know the engine is not running that fast. Sometimes...Today I pull in my driveway after it was doing it all the way home. It goes berzerk coasting. Wants to die and backfire if not easy on the gas. Tries to die at stoplights and rarely does that's the only time the tach reads right is when it is trying to die or taking off fast. 60mph down the highway and it tries to die out of nowhere .I used to think there was a short in the blower motor. Because it would only happen when the blower was running if I turned it off it would stop. I recently pulled the fuse for the heater A/C. Unplugged the blower motor. Now it is doing it more. And I can't make it stop. It has backfired a few times. I know I probably need to do the clean the IAC and TBI. I just can't figure why my tach would be jumping around like crazy if the engine speed isn't. I know if its sitting there idleing at 900 and the tach starts going nuts saying 3500 no 4000 no 2500 my engine idle is not changing.

 

Bolt a big, ugly ground wire directly from the engine to the battery negative, and another one from the same point on the engine to the firewall or substantial body part.

Verify the connections at the distributor, in the distributor, and the coil primary wiring.

Something is very strange in the ignition system.

 

91 Camaro RS. Junkyard 350 from Caprice put in it. I bought it. I've changed plugs, wires, distributor

What kind of distributor did you replace it with? was it just the cap and rotor? thats just a thought to ponder.....When you do a tune-up, one of the things you replace on your engine is the cap and rotor -- these eventually wear out because of the arcing. Also, the spark-plug wires eventually wear out and lose some of their electrical insulation. This can be the cause of some very mysterious engine problems.

 

Yeah just the cap and rotor. Might try that ground wire, When I bought the car the main ground to the engine was loose and he coundn't figure out why it was burning the little ground to the frame in half and not starting. I replaced the main ground and grounded the little one to the frame. It seemed like it got a little better after that for awhile. Then I repalced the altenator and positive cable and wired everything more directly. Like took that stupid hub thingie out. I thought it wasn't getting enough power. No change. Today it was running fine. I unplugged the A/C wires to the pump or condensor whatever it is. And pulled the nearby relay. The one closest to the blower motor. I didn't notice anything not working my tach didn't jump around today. So fingers crossed I can fix that later if it will just run right now. Some guys got a distributor that puts out more power I don't know its some how different I might try that after I clean the IAC and Tbi this weekend. I check back in later. Thanks for the responses.