Got this weird problem I need to try and fix....

Problem: Sometimes when I start my car she will not idle properly. On a cold start she would normally rev up to around 1000 rpms, stay there for awhile until she starts to warm up and then slowly drop in idle to sit around 500-600 rpms.

Now sometimes she will start properly for a second, idle goes up to 1000 and then it goes all over the place, she starts hunting for her idle, drops to 400 or so almost dies, shoots back up to 1000 and repeat. Sometimes she will cut out immediately after she starts, just falls flat on her face after she revs up to 1000 rpms.

Partial Solution: Sometimes when she starts this behavior I can just her a few shots of gas and she will idle right. Sometimes if I shut the car off and restart her it will be OK. Sometimes she will hunt for her idle and find it by herself. And other times she's just find, like nothing is wrong

I noticed that this behavior started happening after I put in my new rebuilt 350 engine. Other than being bored 40 over and flat top pistons its the same engine, even the same casting number but with 4 bolt mains. Only other mod was that I had my stock L98 heads ported but these heads were on my old stock 350 engine and it never had this problem. Not sure if that has anything to do with it...

When she doesn't act up she pulls like a freight train, very hard/smooth accelleration.

Someone mentioned that this could possibly be my EGR acting up, ie: at idle it shouldn't be opened and if so it acts like a huge vaccum leak? Anyone got any suggestions as to what to check...

So far I have checked..

1. Codes set... none, all clear
2. Injectors... all fine
3. TPS ... fine... goes from 0.540V idle - 4.3V WOT
4. IAC ... fine... checked it and it's operating properly
5. Fuel pressure... fine... fuel pump is a fairly new Walbro 255LPH (less than 2 years old)... I have a pressure guage on my Shrader valve and it shows good FP (around 43psi when the key is turned ahead, 36psi when idling).. FP never drops off even when she cuts out

 

Any gurus with any suggestions/pointers for me to look at?

 

Maybe try running some fuel system cleaner through it, then changing the fuel filter (if it isn't fairly new already).

 

already got a new fuel filter

 

Maybe get your ignition module tested. It can cause it to surge around like that.

 

Check your MAF or MASS sensor.

 

MAF or MAP....Sorry, wasn't thinking clearly.