Okay, about a week ago I pulled the throttle body off my car and gave it a thorough cleaning. I also cleaned the IAC really well. I was prompted to do this because my car has been acting up some mornings until it gets into Closed Loop. It would idle fine, but the engine would hesitate and it would accelerate really poorly. Once in Closed Loop, the trouble would clear up and the car would run great.

The car seems to be running better since cleaning the TB and IAC , but now it idles erratically in the morning. It will now idle at 1000 rpm while warming up and after a few minutes will settle down to around 650 where it should be. It never did this before. Typically it would idle around 700 or 750 during warm up and quickly settle in at 650.

Also, after restarting the car when it's warm, it will briefly idle at close to 1000 rpm, drop down to 650, climb back up to 800 or so, then finally settle back down to 650. It seems like the IAC may be outta whack and the ECM is "hunting" to get it under control.

Anyone ever have their car do this?

I'm going to check the IAC tonight and also check the TB for any possible vacuum leaks. Feel free to toss in any $.02 worth of info.

 

Has the computer had time to relearn?

 

Russ,
Yes, it has had plenty of time to adjust. Tom K. has a quick article in the tech section on setting minimum air and adjusting the IAC. I'll probably start with this, then disconnect the negative battery cable and clear the computer so it can start from scratch.

I suspect that the ECM is trying to compensate in some way since I cleaned the IAC port and needle. There was a bunch of carbon in there.


For anyone who's interested:

Idle Air Control
Tools needed:

1. Torx bit # T-20
2. Paper Clip
3. Small Punch

Take the paper clip and open it up and form it into a big "U" shape. Insert the clip ends into the ALDL in the 'A' and 'B' pins.

Turn on the ignition, but don't start the engine. Wait 30 seconds. Now, go remove the connector from the IAC.

Start engine. You are now going to adjust "minimum air". There is a Torx screw on the side of the throttle body. This is what needs to be turned to adjust minimum air, or more commonly known as "idle speed". It comes from the factory with a protective metal cap over it. If the cap is still there, use a small punch to knock it out. Set the idle speed to 450 rpm, rotating the Torx screw clockwise to raise rpm, and counter-clockwise to lower rpm. Once the idle rpm is set, turn off the engine.

Re-connect the connector onto the IAC. Start engine. Idle speed is now once again governed by the ECM, but your idle should be smooth and steady, approximately 600 rpm in Drive (for unmodified cars).

If you set an SES light by having the IAC disconnected, then after shutting down the engine disconnect the negative battery terminal. Wait 5 minutes. This will clear the ECM of all trouble codes. Re-connect the battery and drive the car for 20 minutes to allow the ECM to relearn your driving style.

 

Okay. I busted out the scanner and checked the IAC. The counts are within parameters. I checked the MAF and it is fine. The TPS seems to be fine. I can't find anything wrong.

I then went ahead and installed a new 02 sensor and disconnected the negative battery cable to reset the ECM. After a 20+ minute drive, the car performed well. However, after shutting it down and restarting it, the idle surged between 800 and 1000 about 5 or 6 times then settled right in at 650. I shut it down and refired it again. The same exact thing. It's annoying, but isn't critical so I'll just have to do some more homework and see if I can find anything.

 

Sounds like a vacuum leak.

 

if it was a vaccuum leak, wouldnt the idle stay high, or is the computer able to compensate?

 

Yeah, it's either that or possibly an EGR problem. The car idled fine this morning, but when I tried to go down the street it hesitated really bad and felt like it would stall. Once it warmed up, it ran great.

It could be that there is a small vacuum leak on the TB when it's cool. Once the TB heats up and the metal expands it could be closing off the leak. I may install a new set of gaskets on the TB and see if the condition improves. I'm even tempted to go ahead and buy a brand new TB.

 

Gaskets are cheaper than a new TB. They cost $4.99 for the whole TPI TB gasket set at autozone.

 

Bret, I had similar problems with my 92 though it is TBI. Try replacing the EGR Vacuum Selnoid and see if that helps. After replacing the selnoid the surging was almost elminated but then it just pointed to the other problem I had as well, a bad EGR

P.S. I bought the Selnoid from Car Quest for about $20

 

It does what it can to correct EVERYTHING. Many times it fails miserably in its quest.

 

Buying a new TB won't do anything but break your wallet. On the other hand the gaskets in it might be leaking (one on top one on the bottom and the IAC gasket).

 

Don,
No doubt. At some point I am going to pick up a new TB, but I'd prefer to wait until I have my new motor. This close to Christmas I'm not dropping $300 for one.

Gaskets are the cheap fix and if it is a gasket it's most likely the lower gasket for the IAC plate. I'm gonna inspect the EGR while I have the TB off and see whats going on there. I know this is probably gonna be some ****-ant little thing.

 

Just spray some starting fluid, carb clean, propane.. around where you think you might have a vacuum leak. That should let you know right away where the problem is.

 

I spent the evening replacing all the gaskets on the TB, cleaning it once again, then hunting for broken hoses. I also cleaned the PCV valve, removed and cleaned the manifold fitting and installed a new PCV hose. The CCV hose is getting brittle so it's time to replace it.

The idle surge isn't as bad as it was. I'll have to see how the car runs in the morning when I leave for work. If it's still hesitating till it warms up the only left I can think of is replacing the EGR valve. It's ten years old at the least.

 

Is you throttle shaft loose in the TB? You may need to make up some bushings to put in there if its too worn down.

 

Here's one more for ya.
On our cars the EGR solenoid is normally open, when the car starts the computer closes it, then opens it as neccessary. It sometimes gets dirty or goes bad.
Take it off and clean it with carb cleaner and test it with 12 volts to see if it clicks.

 

Thanks for the tip Don. I am really starting to think it is EGR related some how. I let the car idle for a good 3 - 5 minutes this morning before I attemped to drive it. It drove beatifully and never hesitated.

I also have an OBD I cable on the way from Summit for my Auto Xray EZ-Link scanner, so I should get some better info. than what my old Actron scanner provides.

 

It sounds to me like what you are describing as a problem is normal for TPI systems. The ECM adjusts to a higher idle when motor is started up. Then after a few seconds, it will drop the idle to the normal rpm (600-750). If the motor is warmed up enough to maintain that idle then the ECM leaves it there. If you have an auto trans and shift into gear, the ECM will adjust the idle by raising it so the motor won't die.
Both my TPI cars work this way.
Am I wrong about this???

 

Well, the problem I've been having is different in that the idle will surge, not just run high for short time then drop down. The idle was also bouncing between 1000 and 750rpm. Also, what started this whole process what that my car on occasion was hesistating badly in the morning until it got warmed up enough to hit Closed Loop.

Since tearing down the throttle body the idle problem has settled down. It's no longer surging. I've been letting the car warm up in the morning for a good 3 minutes or so and that seems to prevent the hesitation problem.

This is all a recent occurance for my car. Prior to this it ran very reliably, always idled nice and smooth, and never hesitated. I've had the car for 10 years.

 

Hey Brett, when my car did that, I hunted forever before finding two injectors that were bad.

 

Brett,
Sorry - I guess I missed the irratic idle part. When it does idle irratic, is it usually after cruising for a few miles, then coming to a stop, and then after a few seconds of spaz idle does it smooth out??
If so, I had the same problem with my IROC, the problem was a leaky seal on my tubes (an air leak!!!). I had installed TPIS large tubes which are a pain to get sealed correctly. You may have an air leak somewhere in the TB, plenum or tubes.
john

 

Glenn,
That thought has crossed my mind. The GM manual also makes a mention of doing an injector test for troubleshooting a hesitation problem. One other thing worth mentioning is that when the hesitation has occurred my A/F ratio gauge has indicated a rich condition by pegging the LED lights into the green.

I hope it's not an injector. The ones on the car are the updated '89+ injectors and aren't that old. 3 to 4 years tops. These are the ones I picked up from Dan Gallagher to replace the 24# SVO injectors I ran for a short time. For only $100 they were a great deal from Dan's buddy who works at a dealership.

The car runs fine once it's warm, buuuut my fuel mileage has been kinda crappy lately. I have a unit for test firing the injectors and may have to run through the procedure to confirm their condition. If the plenum ends up coming off I'm gonna replace the EGR valve at the same time.

The biggest pain about this whole deal is that my registration is due in January and I have to get the car smogged. I don't dare take it in the way it's running right now.

 

Yeah, a vacuum leak was my first thought and that's why I replaced all the gaskets on the TB. I also replaced the PCV hose and still need to replace the CCV hose. It never hurts to start with the cheap stuff and work up from there.

The hesitation issue is my main concern at this point. That's the bug that started everything. It could be EGR related or as Glenn mentioned, a bad injector.

 

Brett, The easily way to test first is the oms. They should be 16+ anything 14- is bad. That's how I found mine. The tester that I had for testing the injectors and wires kept saying everything was okay. I used the Accel 21 lbers until I switched to MSD 22's (must stay with the stock range for SCCA).

 

Glenn,
Thanks for the info. With the tester I have you have to pressurize the system, connect the tester to an injector, fire it and record the before and after pressure. All the injectors should be close in pressure drop. The test is kind of a pain and I'm not sure that it's all that accurate for diagnosing a bad injector.

The ohms test sounds better and quicker.

The Accel web site shows a 24# injector for '87-'88 5.7 Camaro/Firebird, yet a 21# for '89-'92. That's not right. The MSD's are the much better way to go, but at $400+ for a set I'm hoping I won't need them. The Accel's are only $229 a set, but I question their quality.

 

FYI, I didn't like the Acce because it's not 16ohms. Everybody wanted $60+ apiece for the MSD until I found Speed-o-motive. $320 for the set. MSD 3PN 2017 A replacement for Chevrolet 5.7L engines. SPEED O MOTIVE 131 N. Lang Ave. West Covina, CA 90670 (626) 869-0270

 

I wouldn't buy anything from that outfit if they had the only ones in captivity (can you spell crooked bast**ds).
I'll explain in person sometime

 

Ahhh Speed-o-Motive aka Dirt Bag Engineering:lala: :lala: :lala:

 

I got my 383 short block from them 6 months ago. I thought they were ok??? Haven't had any problems, and everything looked ok when I put the motor together. I've got about 6000 miles on the motor.
Let me know what you know about em, I'm worried NOW! PM me please
john miller

 

https://www.thirdgen.org/techbb2/sho...t=Speedomotive
More:Speedomotive screwed up on the motor. He ordered a forged 4340 crank.

Speedomotive should be the ones that take the blame for the shortblock. I think I told him to check the clearances when the motor got there, but he was mad cause it was 3 weeks later than they said, and it didn't have the parts that he ordered on it, and he wanted to get it in the car. I've heard bad things about speedomotive, so that's why I wanted to check the clearances before it went into the car. He said they guaranteed their work so it went in the car.
More:
I too had a bad experience with speed-o-motive. Motor was way late and spun a rod bearing within a few hundred miles. Best I can tell is the rod was tapping on some pan rail flashing, I heard a faint tap on start up but thought it might be the Crane Hi-intensity lifters, basicallly variable duration lifters. Their customer service service sucks, pretty much told me I did something wrong since they never do.
This should give you plenty to read:
https://www.thirdgen.org/techbb2/sho...t=Speedomotive

 

Thanks Don,
I had no idea they were screwing people, all I can do now is hope I'm lucky. I didn't pull the bottom end apart before installing the cam and heads, pan etc, but I did check to make sure I got forged rods and crank I paid extra for. I also checked their machine work on the block. My son and I were planning on buying another motor from them for a boat we are restoring, but now we won't, we'll just do it ourselves.

 

Well I didn't know about their work but I couldn't past on their price for the injectors. When I got there, the injectors where in a box with MSD on it and they were in sealed bags with MSD on them.

 

Glenn,
I will keep that in mind. I am still waiting on my OBD I scanner cable and haven't checked the injectors yet. The car is running better though.

The idle is still a little high in the AM, but no hesitation problems and the idle is somewhat steady now, no surging. I did run a bottle of Lucas Injector Cleaner/Top End Lube thru the fuel system and my daily commutte lately may be having some effect as well.

For the last two years my daily commute has been very short - 3 miles one way and my car saw little freeway duty. Since my job situation changed, for the past couple months I have been doing freelance work on and off down in Venice and have been commuting thru Topnaga Canyon and PCH. I'm wondering if maybe my cylinders have some carbon build-up due to my old short commutte and after a few days of highway driving if they are clearing up some. The engine now has 161,000+ miles on it.

One thing though is that my gas mileage is horrible lately. I'm driving approximately 40 miles round trip and burning over a 1/4 tank each day. The canyon section of my commutte may have some affect too since it tends to be a lot of on-the-throttle, off-the-throttle driving. PCH is similar. Still, it's not fun getting gas every 3 days.

Also, I did some homework and I'm wondering if a malfunctioning coolant temp sensor could be my trouble? In Open Loop the ECM ignores the 02 sensor and relies on the MAF and CTS, as well the info. stored in the memcal. A bad CTS signal could explain my Open Loop hesitation trouble. A bad CTS could also explain my poor fuel economy. If the CTS is telling the ECM that the engine is colder than it really is, wouldn't the ECM then fatten up the fuel mixture to compensate?

On an occasion or two, my A/F ratio gauge has indicated a temporary rich condition. Rather than a steady bouncing back and forth, it hung in the rich zone momentarily. Hmmmmm.