Hi,
I just took the car out from winter storage. The car is an 89 IROC, 5.7L TPI with 81k miles on it. The car had this problem when it went into storage but now the problem is more pronounced and has actually led to the car stalling and not being able to start again for 15-20 minutes.

The problem is the car, once hot (say <5 minutes) will 'hunt' or adjust the idle speed +/- 250 rpms from a base of about 600 rpms. The car now gets into these fits where the idle drops low enough for it to stall. I've changed the gas in the car, checked the battery, battery cables, distribuitor, various ground connections, vacuum lines, the IAC, and the TPS. These systems seem fine. I then moved on to the EGR solenoid. Before I put the car away I replaced the vacuum hose from the TB to the solenoid(by the coil). I pulled this vacuum line at the solenoid and pluged the solenoid yeilding no result. The car still has the problem. I now am questioning if the solenoid is that messed up, and the EGR is stuck in the open(?) position? Is there another area I want to check first before I take off the plenum? I havent had a chance to tear into the ESC, thats another thing that has to be checked. The car is also throwing no codes. Also, it seems like the car will hunt off idle if it is at a constant speed up to say 1500 rpms, and when the cruise control is engaged.

This may be a little long winded, but I tried to cover all the info I have. This makes me mad because the car idles fine until the stupid whatever it is kicks in and causes the idle to hunt. If it turns out to be part of the emissions control system.....I may be slightly aggrivated. I appreciate any ideas I just hope Im not missing anything basic. Thanks A lot in advance!!!

Martin

 

vacuum leak

 

Mine did that same thing exactly.

It was a vacuum leak.

 

Check for vacuum leaks, double check all your hoses.
Check your fuel vapor system.
Check for a sticking throttle, on the throttle body.
Check your fuel injectors, resistance and if they are leaking.

 

Thanks guys, Ill go after a vacum leak before I try anything else.

Martin

 

Under the heading of "Vacuum Leak" you could find the obvious things, like hoses, less obvious things like PCV valve, power brake booster, or gaskets, and the truly obscure items like the vacuum reservoir in the fender, EVAP control valve, EGR valve leaking through, etc. You may want to disconnect some devices and cap the fittings to isolate them.

 

I agree with you that these are all less than obvious, but it brings something to mind. In another recent post you took a stand against "ripping all the emissions off".
It seems that problems like this would at least give some justification to remove as many unnecessary lines & systems as one could get away with. I think in many people's minds they realize that having less of this "junk" under the hood will pay off by eliminating many possible problems & headaches.
I don't want to start an argument at all. I'm just pointing out that people are different with different goals & agendas for their cars.
I just don't think there's any point in arguing the point of keeping everthing stock when someone really really wants to strip stuff off. Sometimes ripping stuff off creates other problems, but then I figure that's their fate of choosing their own path.... you know as long as they're happier in the end.
I know you have to agree that a stock fully equipped car has many many times more possible points of failure to troubleshoot when problems come up.
No need to reply on this, just playing devels advocate a bit.
Good call on the possible vacuum problems by the way.


For hunting idle don't forget to check the IAC, and the TPS adjustment.

 

pop off the IAC and see if it is gummed up. carefully decarbon with carburetor cleaner. Reset it .. and cured the problem

Mine was doing the same thing after about 6 months of storage.

I replaced the fuel filter, stablized the fuel, new rotor, cap, plugs. I cracked the pickup in distr. so I replaced it and reset the timing.
I rented a vacuum guage, and vacuum was holding.

Runs extremely smooth now.

 

I checked all the vacuum lines I could find. I also rechecked the IAC. I started the car with the gas pedal depressed slightly let it run for 5 seconds and shut it off. I tried to start the car after this it wouldnt catch and run. After waiting I started the car and pulled the connector for the IAC, the SES light didnt even come on (makes me nervous when the car doesnt know Im pulling connectors?) I drove around and as soon as the car warmed up, it started hunting.

As far as finding vacuum troubles is there any trick to it? Do you just start plugging off various systems beginning with the emissions? The vacuum port on the EGR valve is the size of a pinhole, it looks like any slight loss of vacuum could throw the whole system off?

This makes me wonder about keeping the emissions control systems on the car I drove the car 2000 miles last year. I hate to take anything off but I'm wondering if its worth it. The not driving the car, I'm sure, is also leading to problems. Thanks again for the help.

Still confused....
Martin

 

Use a propane torch (unlit) to check for vacuum leaks. It'll work as long as your hoses are in order. The hoses near the rear of the plenum are usually the first to go. Have you checked your spark plug wires, dist cap and rotor? Also, do check your injectors. That is a common cause of idling issues as well.

It's also possible that your ECM is bad.

I've had vacuum leaks from bad hoses (crumbled on the underside near the distributor though the top side looked fine), bad injectors and bad ECMs. All of those displayed similar problems. The ECM was not hunting on a set frequency. It would just idle at 2000, then drop randomly, or go up randomly, or idle fine.

Bad injectors did do the issue you see. Check your injector resistance. It's quick. Pop off the injector clip using some needle nose pliers (squeeze the metal clip in towards the body of the injector and lift up), connect an ohmmeter to the two nodes, and read the resistance. You don't need the ignition on for this. It should be high, around 16 if your injectors are stock.

 

Thanks 91Z28-350, I'll get at it with the torch tommorrow. The injectors should show a nom. resistance of 16 ohms? I'll check that in the light too. I also have the original memcal chip for the car so I can swap that in. Im less likely to believe the whole ECM is shot then something as simple as a corroded ground somewhere along the line. I can only wonder at what could destroy the ECM. Looks like I'm going to have to start looking for non obvious solutions to this one. Thanks again for all the advice and keep the ideas comming! All the experience available through Thirdgen.org is always amazing.

Martin