what can cause a motor to surge 8-900 rpm when at idle?

 

i would start searching for a vacume leak somewhere first

 

Vacuum leak, leaky injectors, bad 02/02's (depending on what set-up you have), ignition woes, MAP/MAF on the fritz.

I would check for vacuum leaks first and go from there. You shouldn't have any problems with your 02 yet unless you re-used an old one or the wire has since become damaged.

 

hey man gl with that problem when do we get to see the new project?

 

My guess would be a supercharger

 

soon enough guys.


the plugs, wires, cap, etc is all new. the injectors have just been flow tested and checked to be sure. it's a SD car with a 730 ecm. everything on the scanner tests out good in the right voltage ranges so i can't figure it out. tried to test for leaks but i don't know what it should be at and i can't hear anything nor does any of the old tricks to check work. no matter how much timing i pull or add as well as fuel nothing changes...

so this is the basic list then?
electrical
fuel
vacuum
sensors
computer


i'm at a loss...

 

Use a propane torch (not lit of course, I feel the need to add this for other people that may read it and do something dumb) and run it along the manifold edges and any other mating surfaces that might have a leak, just listen for a rpm change when it sucks the propane in!

 

ok it blew up my car... now what? i tried that with a similar form of starting fluid back before i asked the question....causes a surge straight into the TB but nothing anywhere around the intake....

 

i guess the surge is gone now,.............

 

good one....actually when I was typing that post I had that mental image of one of the less experianced members car winding up looking like that lol.
You could still have a leak on the valley side of the intake, no good way to check that ......... or it is something else....long shot since it is TBI have you checked the injectors with the timing light just to make sure the pattern is good?

 

it's speed density TPI. the injectors have been flow/bench tested and are good. the scanner is showing all sensors in the right readings as far as what they should be. the car is basically fighting with the cpu as it seems to go lean. i've tried pulling/adding spark as well as the same with fuel.

as i said the car worked when i drove it into the garage, swapped miniram for superram and now it has problems. spent time with the chip but nothing seems to work right now? i know they are two completely different intakes but i would think that since the chip worked well with the one setup it would at least be in the ball park which it isn't.

 

Also another long shot is did you remove/plug all of the vacuum lines to make sure of no leak in the line or at the accessory like the brake booster, ect.

 

Sorry I should have realized that, I remember you looking for a intake. lol..... Now I can see someone holding a fuel rail pointing a timing light at it

 

yes but i will double check them as well....

i appreciate the suggestions, as little as they are every bit helps as we often overlook when we are tyring so hard to fix a problem. if you or anyone else comes up with anything let me know, i'm going to step away from it for a day or so just to think about it.