coming to a stop for about 5 seconds holds at about 1400 rpm then slowly drops to about 800. i changed the aic no difference throttle linkage seems ok ?

 

clean and lube

 

Well it probably shouldnt be as high as 1400 rpm's, but watch your speedo, mine does somewhat of the same, the idle is still high when I come to a complete stop, I noticed my speedo was still winding down to 0, then once it hit 0, the idle dropped down. look and see if thats what yours is doing.

 

Check volts TPS mine was changing every time I would check them .54V I like mine @ .60 when mine was doing that I would get a reading of .76 one day the next .49! Changed out TPS salved my problem! Just saying!

 

Car has high idle (1000-1100 when decelerating until 1.5 to 2 sec after full stop then drops to (650-700). Does NOT drop with initial brake input.






Still high after:
1.TBI cleaned and shaft bushings installed
2. Air control replaced and adjusted properly
3. TPS replaced and adjusted properly
4. checked for intake leaks
5. Timing set to 8 degrees BTDC with ESC disconnected, I know book says 6 but those that seem in the know say 8. By the way set at 6 makes no difference in this problem. I notice timing with ESC connected is about 13-14 degrees BTDC
6. MAF relays replaced
Runs strong at power and cruise but sometimes shifts to overdive early ( it's an auto trans ) believed to be separate issue?
Any help would be greatly appreciated.....as it's getting on my nerves a little!!!!

 

does that one have the tv cable? might ajust and lube

 

If your talking about the cable that operates the TBI yes, but it's clean and free.

 

Just a idea! When is the last time you have looked at the advance springs and weights under the rotor in the HEI?

 

I have replaced rotor and cap but saw no springs or fly weights. I understand all timing is set by the ECM......is that incorrect?

 

Is this a manual shift car? My experience is that they do some of this by design for emissions. Mine will idle about 1100 until the car comes to a complete stop, then settle at 800. Also my return spring was getting weak so sometimes it wouldn't drop all the way. I put a little helper spring on it.

 

My 86 does the same basic thing though it didn't when I got it. I suspected the IAC valve after a while and while under the hood one day gave it a couple of taps with a plastic faced hammer and it started dropping when stopped like I thought it should. I plan to change out the IAC at some point but for now it's working so it's not a rush item for me.

 

And you know this numbers, how? Stock tacks are inaccurate. I'd get a scanner and see what the ECM is seeing. Mine was 3-4 hundred higher. It didn't match my timing light with tach or the scanner. Scanner and timing light match though. See later for scanner.

1. Cleaned how? Did you take the top plate off, take the IAC solenoid off and clean the pintle GENTLY? Did you take off the IAC housing and clean it and the passages in the TB?

2. How? Book method relies on everything being right but that adjustment which is why I don't use it for anything.

3. As verified by scanner?

4. How? Either run smoke through it or use scanner to verify.

5. 8 degrees is to make it more peppy but you dump 2 extra degrees all over. I usually prefer to have it set through the chip during a dyno tune which is done once I have done a radical enough set of mods. Say entire intake and headers, heads and cams, bored and stroked motor.

6. Check TV on the throttle body. (Throttle Valve or Transvestite, your choice).

I would say your next 2 acquisitions would be an FSM and a scanner if you don't have one already.

Items 2, 3 and 4 should be done with a scanner. I set it to idle, see what the IAC counts are and adjust. More than 20 means the IAC is opening up to let in more air. Screw in the adjustment screw. Less than 20 means it is too open and you need to screw the adjustment screw out. Rev and recheck. Say you keep adjusting it out till there is no more adjustment and it still reads 0. That means there is way too much air going in. You probably have a gasket or hose leak. TPS setting is based off what the ECM sees in that case.

 

Why not clean the pintle, passages and reset? Of course you need new gaskets. I don't reuse condoms or gaskets as a rule. That is, unless it is a valve cover gasket that is meant to be reused.

 

1. Cleaned means disassembled, vatted, brushed and passages verified open with compressed air. IAC was replaced with new, (I said Air Control valve, sorry).


2. Book method requires everything to be just right so you don't use it? Are you talking FSM? If so why have it?


3. Yes, I have a scanner and it works well.


4. I have no smoke machine.......yet.


5. This is a barn find, original with no mods....and I want to sell it as such. I just want it to run perfectly before it sells in March. I will scan and adjust for 20 counts....


6. So why would the Idle hold high at 1100 with ignition advanced to 14deg, and then drop to 700 and 8 deg.......???????


This thing is getting on my nerves.............

 

Just checking. Many forget to take off the housing and clean all the passages and the housing as well.

Correct. I don't use that technique because I am not stock and my command idle is about 900 and even if I were 100% stock, it assumes you have no other air leaks, timing is right, tach is accurate, etc, etc and we both know what ASSUME does.

Get engine to stable operating temp and in closed loop, shut everything off but the engine to check.

I would say that the timing does alter the engine speed. AFAIK, it will try to achieve the command idle to a point and then, it is maxed out. For example, my credit limit is $100. Past $100, it declines. I'd set the base to 6 and adjust the minimum idle speed and see whether it holds steady. My moron "mechanic" somehow got the car to run right at 19 degrees and it seems to take a bit at a stop light to come down in idle speed. Set it to 6, set IAC and it was steady. Go figure. When I needed the advance, it came with the dyno tune.

 

Mine runs great at 8 with tons of power, no ping. Setting it at 6deg makes no difference but cuts acceleration a tad. Just can't figure the "hanging" idle.........................any other suggestions would be greatly appreciated .........

 

Does the ECM agree? I'm curious. Some say the L98 tunes are too conservative from GM and some say that the ECM has seen a little more knock and retarded the timing to compensate. IDK. I just set mine to whatever base and have the tuner build the tune around it.

Try setting it back to 6, have the IAC cleaned and adjusted and make sure there are no air leaks. If you cannot set the IAC using IAC counts, you probably have a leak you need to fix first. How are the injectors? Have they been tested and cleaned recently? Plugs and wires? Any spark leaks on the wires? How is the cap and rotor? Fuel pressure and does it hold during a WOT test in gear?

 

1. Again, IAC is new
2. No vacuum leaks I can find.
3. Injectors are new Bosch F3s from FIC
4. Wires, plugs, cap, Rotor, Fuel pump (42PSI), Fuel Filter, FPR, all new.


This car did not run when I bought it "Cheap" out of a guys garage where it sat for 2 years and I have put into running order over the last couple months......It now runs great except for the hanging idle.

 

I have never had this issue since I clean the throttle body and take off the housing but others have said that if there is gunk there, it might not allow the pintle to close all the way which is why I was curious if that too was cleaned. I do mine every 3 years with the injectors out for service. Without the PCV and EGR so I don't know but when I took apart the stock system when the motor was being removed, I did notice some sticky stuff in the TB hence my every 3 year cleaning program.

2. See what the ECM sees as IAC counts. If it is 0, it means that there is too much air coming in either a leak or the throttle plates are too open or both. That is why I said that if you turn the screw all the way out. rev it and you are still 0, you might have a leak somewhere. I have used that method to see if I have a leak instead of going on a "snipe hunt" only to find there is no leak. Incorrect timing and incorrect adjustment based off feeling was the cause of my hanging idle by the old school carb idiot who called himself a "mechanic". When I couldn't solve it, I brought it to Lingenfelter who did. Later he asked me why I had timing set so high and the base idle was way out of adjustment.

I bought mine cheap too. PO butchered it up and I had to undo all his "ghetto engineering". I'd say put him against a wall at dawn but I am not that kind a person. OTOH, I paid way below book value so....Still pissed at it. Thankfully, I sold the motor and trans after I transplanted the engine and trans from the F-body that had just gotten tuned 2 weeks before and I was starting to enjoy it. New shocks, new FX3 actuators, replaced "missing" bulbs on the DIC, and removal of his "anti theft device" (basically a push switch because he was too lazy and stupid to change the starter relay) and the car was more to my liking.

 

I will check IAC count today or tomorrow.....I'd like to ask your opinion as this is the only vette I've ever owned.....what might it be worth with the following info:
1989, stock, always in Texas, no rust, runs great, new paint (2800.00) 76,000 original miles. You can see photos on auto trader as I'm in Keller, Texas. Everything works except the auto temp heat control....Electronic dash is perfect. I like the car but my truck is pissed it has to sit outside and 4 cars is too many. Thanks very much for your input.....