So last night I finally got my 95 sohc into my 98 Neon and all went pretty much routine except for the start up, which was hard because I had run my Neon on empty prior to pulling the other engine out so once it did run it ran like a tractor because it was running on fumes. Now fast forward to today I got some gas for the car, enough to get it almost to quarter tank and tried my luck. I had to prime the fuel rail close to 20 times before I even attempted to start it, then it ran sort of rough once more along with a pulsing idle that went from 1500-2000 Rpm.

I let the car warm up figuring that since its been pretty much 5 degrees when I got done with the motor that maybe the IAC was froze up or something had ice in it as I had left stuff outside as I was working on it. So its idling and backfiring a bit, then all of a sudden by itself it shot up to 8,000 Rpm faster than the time it would take a hat to fall out of your hand and hit the floor, it reved probably as fast as my ZRT600 Tripple snowmobile and sounded much the same it does at 8000+ Rpm.

I'm wondering why the rev limiter has NOT kicked in, and why a IAC that worked great prior to parking the car (I used all my good working 98 equipment on the 95 block & head intake & tb and all sensors). I tried my stock pcm, did the same thing, then put back my dohc pcm and also had no rev limiter. Now I know what a Neon motor in my car with my exhaust system sounds like at 7,000 Rpm and this sounded like a snowmobile engine with how fast it reved and sounded, so I believe it really did hit 8,000+ Rpm.

I pulled this motor and did everything in my cold snowed up driveway, I was thinking maybe something might be froze, so I took the tb in the house and let it thaw out and I lubed it up and still the same thing I'm stumped! I also have a hard time believing it'd rev up so quickly with no butterfly action out of the tb and just breathing through the IAC hole...Maybe an intake leak? So now it doesn't backfire anymore it just goes up to max rpm as fast as it can, its a snappy responsive little engine I can tell that much and I didn't even get to put it in gear yet.

 

Thanks for the help guys....lol

Anyway figured the problem out, intake cracked in the 5 degree weather we had when I was putting it on the motor. The sealing surface was like a banana. Put new intake on with copper permatex to aid all the sealing surfaces and it purs like a kitten.

So mental note guys, warm your plastic intakes up a bit before putting them on outside in cold weather.

 

My neon once went crazy, the engine started to rev on its own, I checked that the intake pipe was sealed, if air leaks in the engine behind the air filter is like pressing the gas pedal, is gonna suck in a lot of air, so it ended up being the TPS throttle positions sensor. It had gone bad so the engine would rev on its own, first I disconnected the wire that connects to the sensor, n drove 3 minutes to my house, I bought the sensor n replaced it, took no more than 5 minutes to do it,

 

On some throttle bodies its not so fast when you strip the bolt head because those steel bolts into aluminum likes to stick the bolts in very tight lol about half of the ones I've taken apart I've had to easy out them or just re-tap. If all goes as planned it can be very simple and fast.