89vettefromhell

ok when the car starts up its fine... idles at 8-900 Rpms... when i drive everythings fine.. no falling Rpms or anything... but as soon as i let off the gas.... it dropppps like a lead ball off the empire state bldg.... it will go from 3k to 500 and wanting to stall in seconds... im not sure what the issue is here... it has been sitting a while not running... could it be old gas??? i recenltly replaced the fuel pump and relay.... could it be injectors????



on a side note.. anyone know how hard to install an adjustable fuel pressure reg on a 89???

bogus

it has all the symptoms of a dying Idle Air Controller (IAC). The IAC is on the right side (passengers) of the engine, on the lower corner of the throttle body. You have to remove the TB from the intake to reach it.

As for the AFPR, remove the plenum, the runners, and replace. The FPR sits at the rear of the intake, between the rails.

89vettefromhell

ty bogus... i will try the IAC! if that doesnt work... then ill try something else!!!

89vettefromhell

ttt ... still would like a few more opinions!

RRT vette

I would suggest to attach a fuel pressure guage to the schrader valve on the fuel rail. Turn key on and note pressure, start car and note pressure. Tape it too your windshield and watch it as you drive and note any fall in pressure. Report back

rick lambert

Close RRT-after you attach the FP guage-turn the key on, if the relay is working the FP should come up-somewhere around 40#, turn the key off and note how far and how rapidly the pressure drops! Report back!

RRT vette

Thinking it might be a leaking injector. .


Have you bought a new FPR to install, already?

goldeneye_vet

I'm with bogus on this. Sounds like the IAC is going south on you. In your FSM there are charts to go through to test this and verify. Good luck!

89vettefromhell

yea i just got a AFPR, it looks as tho i can actually get to it without taking off any of the intake aswell ... i was just wondering if you HAD to take the intake of .. or if anyone has installed one without taking it off ty much guys im gonna try it all

TheCar

If your still running stock computer programming get someone to burn you a custom chip. The best money you can spend. Thats what it took to cure my idle problem.

mseven

I don't think he needs a custom chip from just putting on duals.
You say cold it idles at about 800, that sounds a little low for open loop. So after it is warmed up it then drops way down, to me that sounds like IAC (as Bogus already stated), or the way the min. air (idle has been set). Other things would be: TPS voltage should be looked at, where is the timing set. That along with a look at the fp as Rick said, is where I would begin.

On a side note, you will have to remove the plenum to install a AFPR, get new gaskets etc. if you do this.

jan-erik

Hi.
I have an 85 and they are prtty much alike when it comes to idling problems.

The first thing you should do is to thorougly clean the throttlebody inclusive the IAC channels and the seating for the IAC stepmotor. The stepmotor you easily can screw off the throttlebody. Pour carborator cleaner in to the channels and let it soak for awjile and then if you havee something to mechanically clean it is good. You may also take off the cooling water channels. Then you will get to the seat of the IAC. Carbon deposites is a large reason for that symptom.

The alternative 2 is that you have a vacuum leak. Check all the vacuum hoses and runners.Leakage where the runners meat the plenum and intake are asources for vacuum leakage. It can be checked by sprayig startgas or propane around them when the engine is running. If there is an increase in the rpm you have a leakage and should change a gasket. Check also the PCV valve if it operates properly. You should hear the small bullet inside it rattle if move the valve bac and forth near your ear.
If this is not enough it might be the EGR valve.. The vacuum part of it you can check by applying vacuum to the vacuum input and it shall hold it for at least about 20secs. Mine was faulty. It might be the valve inside it . That is more difficult to check.

This tuning made my car prrrr as a cat on idle.

Good luck from
Jan-Erik

RRT vette

These guys have offered good suggestions. These are easy steps to take and won't cost anything except for carb cleaner. IMO I would check the fuel pressure first if you have a guage (easiest) and make sure the PVC valve rattles when you shake it. Then remove the TB from the plenum and IAC from the TB for a good visual cleaning. You will need a voltmeter for the TPS adjustment and a torx bit for minimal idle adjustment. There have been several posts here on the steps needed to take for adjusting the IAC, minimal idle, and TPS and should be done in a certain order.

89vettefromhell

thanks guys for all the suggestions... i am definitly going to check EVERYTHING that you guys said.... and most likely ill just replace it all.. couldnt hurt anything!!! since it hasnt been replaced and ALL of its from the all original 125k miles!!!

pavell

don't throw all that money at it yet.

i had the exact same problem, and a new fuel filter fixed it!!

change that first!!

RRT vette

Most of the parts are probably good. You just need to troubleshoot to find the real culprit. Spending money on parts to replace just because of them having 125K miles is a big waste. This is my opinion but if you have plenty of money have at it. Just follow all the suggestion and report back with more info. This forum is a excellent tool and can be utilized for things not understood.

Red Tornado

i just went thru something very similar.

turned out to a failing IAC motor + the TPS was going south.

the IAC counts were like a ping pong game as verified by tts datamaster, so i replaced the IAC motor. this solved about half the problem, it stopped stalling so often but the rpms at idle kept plummeting over & over, and would finally recover after about 20-30 seconds.

the voltage for the TPS was .47v, its supposed to be .54. a new TPS (mine's non-adjustable) solved the rest of the problem.

89vettefromhell

i know the old saying if it aint broke dont fix it... but if you can get better parts why not... i figure im throwing a few new things on the Intake system so its gonna be off for a little while anyways ... might aswell replace some stuff.. as for the fuel filter... it has 500 miles on it

mseven

I can apprecitte the IAC, TB work. I would suggest a couple of things.
If you do that, get a gasket set and some TB cleaner. Take it apart and clean it all real good paying attention to IAC area and all carbon build ups. Spend the time and follow directions (FSM) to installing the IAC making sure the pintel is retracted. This is a fairly easy procedure that gives good results. Check or re-set min. air (idle) setting. Check TPS, testing w/a vohm to see if there are any "dead spots".

I would also go through some other basics. While you are in there, inspect igniton wires if burnt by valve covers etc. Check for for vac. leaks (all lines etc.) inspect or replace PCV, and check the timing w/est disconnected. The best is to have a handle on what's going on in the suspect areas.

89vettefromhell

gotcha... so far out of everything ive changed the PCV valves 2 days ago... i just ordered a IAC valve... and i just had my Mechanic check the TP Sensor and it came out fine... now i will try resetting the Min air setting like you said and im going to really clean up the TB and get the gaskets as mentioned!! .. Update tho... car is running better already after 120 Miles and Fuel System Clean.. no stutter what so ever after PCV vavle