any ideas? i just replaced the fuel pump which didnt seem to effect my high idling issue (didnt think it would, but the pump was giving me 7psi.. so i figured it should be replaced- car is a whole lot more powerful, but still idles high)

i have a feeling its vac related. someone said, check the MAP sensor and the intake manifold gasket.... so before i go tearing up the engine or spending $45 on some part i might not need, any way i can test these things? i have a feeling that the gasket will be hard to "test" so ill try testing the MAP sensor first..

any kind of voltage i can check or something, maybe take it apart and clean it out? i duno.

 

MAP sensor has 3 wires. 5V power, ground, and MAP sensor signal. Signal should be around 5V at key on, engine not running, and somewhere around 1V at idle with a stock cam.

Or, get a scantool, and see if the MAP value reported by the ECM makes sense. (95-100 KPa at key on, engine off; 25-35 KPa at idle would be typical)

GM used the same 1-bar MAP sensor on about a zillion cars, so next time you're in a junkyard, grab a yourself up a spare or two.

FWIW, MAP sensors don't fail very often. I'd be looking for other causes first, like maybe a vacuum leak somewhere else.

 

yeah i really didnt think that hte MAP sensor would just fail like that easily... im thinking that maybe there is a vac leak out of the intake manifold gasket... i might pickup a vac gauge to check the vacuum pressure..

any idea what stock TBI pressure should be? does the diameter of the lines effect this reading at all? cause i replaced a lot of the brittle plastic hard lines with flexible rubber hose and i dont know if its the same diameter or not...
thanks!

 

Get a vacuum pump with a gauge and hook it up to the MAP sensor. If you can monitor engine parameters, just watch what it reads. Other wise you will have to use a scan tool or a digital multimeter.

 

You can test the MAP output voltage at a known vacuum/absolute pressure level. Voltage should be close to this:



If you have a high idle, it very well may be a vacuum leak. Don't overlook the brake booster. Disconnect and cap the line to eliminate that possibility.

Remember that the PCV valve is little more than a "programmed vacuum leak". I had a similar high idle episode on a TBI that turned out to be an incorrectly calibrated PCV valve spring in a brand new valve. Pull the PCV and cover the end with a cap or piece of tape, and see if the idle returns to normal.

You could also have a sticky IAC, or debris in the IAC passages.

A slight EGR valve leak can do the same thing.

Binding throttle or an improperly adjusted minimum air position would be another thing to check. Set the TPS while you're there.

 

vader, i have a new IAC, and the TPS isnt adjustable... i just got a new PCV and checked the brake booster cable, ill try capping them both off... unfortauntelly at the momemnt my car is apart due to me putting in a new intake manifold gasket (i figured what the hell, nothing better to do right now ahhaha - and i hadnt ever done it before so for experience) anyways.. once i get the car all back together ill see if maybe there was a vac leak in the plenum if not, and the idle is sitll high, ill cap off those lines like you said and see if it drops. the EGR is also in the back of my mind. i can move the diaphram with my finger but its very very rough.... like not smooth moving at all. which makes me think that it could not be coming down all the way... is there a way i can bypass this unit? maybe take it off and see if the idle decreases? thanks!!!

 

If you're already removing the intake, pull the EGR from the intake, carefully inspect and clean the pintle and seat, and clean the exhaust passages of any accumulated carbon and coke. It can't hurt, and may be your last best chance to get at the EGR. Remember to avoid any type of solvent cleaner on the EGR, since the pilot diaphragm has an elastomer seal that is made of a heat resisting compound that doesn't resist solvents very well. There is a small pilot passage from the pintle to the pilot valve, so anything you spray or wash in there will likely get to the diaphragm.

 

Hmm...I would just take it to an auto shop and have them connect it to a "smoke leak" machine I had that done on mine recently, makes your problems a lot easyer.

 

hahah dangit i just finished reinstalling the intake... i could take it back off but then i would need to get some more RTV to seal it again...

BTW what is the RTVs purpose? is it just to keep stuff from getting in there or is it really supposed to seal the whole area air tight? the gasket didnt come with a lot of it and im not sure that the whole china wall has a solid seal.... maybe i should pull the intake off anyways....

how hard is it to remove the EGR from the intake with the intake on the car? i havent reinstalled all of the connectors and accessory stuff yet, like the TBI