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.
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ohh yeah everything else on the engine is from the original 305 tbi. Just the engine was swapped.

 

i am not really sure but here was my first thought.the tach is run by the distribtor or coil not postive which.so i would check in that area for problems.it could be as simple as a wire not making a good connection.that would definetly cause it to want to die and that is were the tach gets its signal so just a thought.maybe something in the dist. is breaking down.maybe someone on here has had problems in their dist. and can tell you how it acted and what they did to fix it.

 

i would try timing it.....if you havent... it would take more advance for the distributor to function on a 350...if you timed it make sure the vacuum advance is hooked up right. if it has vacuum advance.

vacuum vacuum vacuum.........check the vacuum.......the only reason i say that is because i just had a nightmare of a time with vacuum and know first time that if its not routed right **** like you just explained can happen, and does happen,....the only thing that i cant figre out is the tach???

check the idle air controll valve.
is your throttle position sensor hooked up?

 

Throttle poisition sensor is hooked up but don't know if its good. The ignition control module went out cost me 250.00 at the rip off shop. But the promblem is still there it backfire alot and shot a backfire out of the TBI. It doesn't want to run at all. So I'm going to try to check the timing. Maybe the whole distributor is bad????? I'm also going to make sure the wires all are run properly. Replaced the idle air control valve. Also had to have the VAT system replaced 600.00 for tow and system at the rip off shop. Now broke and it still don't run right. I was thinking maybe the fuel pump is going out but I don't think it has anything to do with tach jumping like crazy. it jumps around more than it did then and if I turn on anything like radiator fan or blower motor it dies and won't even idle. It seems like timing advance is messed up or bad distrubutor.

 

when did you last replace the alt?