Its an 88 IROC with a 350.
The idle always seemed kinda lopey, even when I bought it. I put headers on it and now it seems to stall sometimes while stopped.
I thought that maybe the fact that there was barely any backpressure with open headers made it stall but I just got my exhaust on and it still stalls. When I come to the stop I can see the oil pressure gauge go almost all the way down and the idle jumps up and down. I thought maybe it was the Idle air control, but I am not sure how to check it without buying a new one. I have an old scan tool that I could probably get any readings if need be. If anyone has any suggestions I would appreciate it.
Thanks.

 

Well I sprayed around for vacuum leaks and couldn't find any. What else could it be?

 

Ok, well thats cool. I just put headers on the car and the 02 sensor went from the top of the exhaust manifold and now it is at the bottom of the header. Will that cause the idle to be like that?

 

I had that problem when I had a 305. I replaced the TPS, IAC and plugs and wires. That fixed the problem for a while and then the car just died on me out of no where. Wouldn't start. So I replaced the Cap and Rotor and the Coil. Still nothing. Then I replaced the Ignition Module and have had no problems since.

This might not pinpoint exactly where your problem is, but my situation was close and it may give you an idea of where to look. If I didn't stay on top of the RPMs at a light, it would stall. High idle when I started the car, and then the lopey idle at temp. I also had drivabilty problems.

 

Could also be an O2 sensor that, since it has moved farther away from the exhaust port with ther new header instalaltion, is no longer getting hot enough exhaust gas to accurately report to the ECM> You might try one of the AC/Delco heated O2 sensors. There are lots of posts here with similar problems after headers were installed and have switched to a 3 wire heated O2 sensor (I'm one of them).

Good Luck!!!



- Vern

 

Can you buy them at regular auto parts stores?

Also, are they easy to install?

 

Yep! Just get an o2 sensor for a early 90's Pickup with a 350 (like a 93 or so). I will come with 3 wires and a connector. Usually one wire is white and the other two are the same color (black if I remember right). Regardless of the colors, 2 will be one color and the 3rd will be a different color. Take the one colored all by itself and splice it onto the existing harness wire going to your one wire o2 sensor. The 2 wires the same color need to be run one to a good ground, preferably on the engine, and the other to a wire that is hot only when the key is turned on. Doesn't matter which one of those two goes to ground and power, they are interchangeable on that. I actually found a female harness connector for the o2 sensor to plug into and wired that in., that way I could easily change o2 sensors down the road if I needed to. It's best if you solder all the connections, too. Look at the Ac/Delco o2 sensor and if it has AFS-74 as the number stamped into the actual sensor then you have the right one.

Hope this all helps, and Good Luck!!!


- Vern

 

Alright, put my new wires on and new heated O2 sensor in. No improvement.
However, I was told I can check the idle air control by starting the car, unplugging it and seeing if the idle changes. Didn't change whatsoever. Then I hooked up my scan tool and it read 144 for the idle air control.
Anyone who knows about these idle air controls, please chime in.

 

Sounds like you should pull the IAC and clean it. They have a tendency to carbon up and stick sometimes from the EGR. I used brake and carb cleaner on mine, though I admit it continued to intermittently give me trouble until I replaced it. But cleaning it might be a good first step just to see if it makes a difference. Only other thing I can think of is a major vacuum leak, so you might check all the vacuum hoses and runner/plenum/throttle body bolts.

Good Luck!


- Vern

 

I just took out my Idle air control and it has tons of carbon on it. I mean caked. So I think I am going to make a trip to the auto parts store and get a new one.

 

HURRAY!!! Hopefully that will solve your problem! Be sure to let us know, but if the IAC is that caked up replacing it is a good idea anyway IMHO.

 

Well I got the new IAC installed. It seems a little better and it hasn't stalled yet. I haven't really taken it out though cause it is pouring out. It still idles crappy though. I wanna say it is at 850-1000rpm and still bounces.
When I installed it, all I did was push the pintle down a little bit, but couldn't get it any further down. Then I just put it in and fired it up. Do you have to do that little connector thing in the tech articles?
Also, my scan tool says that my TPS is at .56

 

I'd try the minimum air procedure for setting the IAC up...

https://www.thirdgen.org/newdesign/tech/tpimod2.shtml

 

So I absolutely have to mess with the idle screw?
Will that make my car idle better?

 

TTT

 

Setting the minimum air can help the idle smooth out.. Also if the idle is set too high (with the set screw), it can cause it to be out of range of correction by the IAC, causing some funnyness/lack of idle control... I assume we've checked for vacuum leaks already, right?

 

Yes I checked dozens of times for vacuum leaks. I would mess with the idle air control screw, except the nitrous plate is in the way of it.
Any othe suggestions?

 

Ok, I replaced the fuel filter too and nothing happened.

I am starting to wonder now though. I got the rest of my header job finished at a local speed shop(couldn't line up the slip tube). Well they redid all my wires going by the starter, but they really just kinda hacked them up and put some butt connectors on them. Could this be causing all my problems? I don't want to replace everything in the car when it could be this.

 

Not sure about the hack job on the starter wires, but I had similar problems as you. Humor me and pour a bottle of fuel injector cleaner ($5) into your tank and tell me if it improves the idle and driveability after about 25 miles.

This was the case for me, so I am in the process of swapping fuel injectors. Were you fouling and plugs? Did you do a cylinder compression test?

Just a cheap idea that if it has no effect, doesn't set you back big bucks

 

Well, I put a whole bottle of B12 fuel system cleaner in there and also ran a tank of 100 octane. I don't know about the plugs though, because I only have a few hundred miles on these.

 

I am still pulling my hair out over this problem. It is now back to stalling out at stop lights.
Does anyone know if a bad oil pressure sending unit will cause this, because mine is leaking a little.

 

New plugs don't mean good plugs. You would be surprised how many new plugs are bad. It takes very little impact for the insulator to crack, but still stay together, which will cause problems.

Best test I know of for spark is to pull one plug wire at a time while the engine is running. If it's bad ignition for some reason, when you pull the wire off the "dead" cylinder, it won't affect idle.

I'm sure low voltage will mess with the injection system, however, if you can start the car, and it runs, I seriously doubt that is your problem. However, I would go back to the shop and beat them silly for cutting wires they have no business cutting, and doing a bad job of putting them back together. Just wait until those wires start to corrode or break, you'll have all SORTS of fun trying to figure that out, if the vehicle doesn't leave you stranded somewhere.

Sorry for the rant, I just can't stand seeing people pay money for that kind of "service".

 

Well that shop I took it to, put the plugs in. I would think it would do it when I am driving too, but it doesn't. Only sometimes at idle. I am currently battling with the shop to get my money back, so I can pay to have someone else to fix it. Long story, but they keep lying. Check out the Chicago board for my post if you want to read.
Anyway, I just found my oil pressure sending unit sensor unplugged and I plugged it in. I found another sensor by the back of the distributor, but I don't know where it goes
http://img36.photobucket.com/albums/...a/P1040236.jpg
Help me out if you know where it goes please.

 

Can't help much on that ID picture...looks like maybe it's for the EGR solenoid? Someone else can probably ID that positively.

As to not noticeable when you are driving....a vacuum leak (for instance) is very noticeable at idle, but if "small", unnoticeable while driving. Ignition miss is the same way...you can be firing on 7 cylinders, have a fairly poor idle, yet at 2000RPM's, you won't notice or feel any difference. (Well, you might, but the difference at idle will be much more noticeable)

 

That definitely looks like the EGR solenoid. And it's supposed to have 2 vacuum lines connected to it. THis could be part of your problem....

One port is supposed to connect to the EGR valve. The other port goes to the throttle body (underneath port on the driver's side). If these aren't hooked up you probably have a major vacuum leak and this could be your idle problem. There is also a thing on the back side of the EGR solenoid that looks like another vacuum port, but it really isn't. It's a breather port, so don't try to connect anything to it. Is the electrical connector for the EGR solenoid plugged in?

 

Yup, that definitely is the connector that goes to your egr solenoid.

 

It doesn't reach that far.

 

i dont know about what that plug is but i have a very bad idle problem it bounces just like yours and sometimes dies

i changed the plugs, wires, cap, rotor, coil, distributer, iac

check my maf sensor and that is working fine, checked the tps and that is fine and still have the problem so i took some intake cleaner and cleaned the intake out with the engine off and with it on(inorder to do it when its on you must unplug the maf and the air hose and spray into the tb

i also used some gm top engine cleaner and when it was idling i pulled the vacume for the brakes and pored it in per the instructions and until it stalled then i restarted it and it was smokin like crazy and blew out all the trash on the highway

i also put some techron in the take and that all helped alot but still shakes and bounces but not as bad

so im going to clean the injectors myself(do a search to find out how)

it has to be fuel related in my case

i will keep you updated and you do the same for me

 

I have the same problem with the rough idle. Check your injectors for a ohm resistance test. Found out one injector is bad and going to have to replace. Will tell you on wed if that was the problem.

Injectors should have a min of 10 ohms. All injectors of mine had 16-17ohm and one was 9.3??!!!

LB9GTA

 

my injectors range from 17.7-18.2 does anyone know if that is to high because it sound like it is to me

can that be part of my problem?

 

If the number was low, that would be the problem. Your injectors are good for resistance, but that doesn't mean that the pattern is good. A leak down test is good for leaking injectors too.

LB9GTA

 

im going to take them out and clean them

while there out i will port the intake

 

Yeah, that is for the EGR Solenoid. Only if I could move it over about 4 more inches.
I don't know if it matters anyway since I don't have any smog stuff on my car.

 

How do I test the ignition module?

 

Remove the module and take it into any parts store. They should be able to test it (little ignition module tester box deal)..

 

Well I took it out and here is what I found. The wire looks all corroded. Maybe this is my problem?

 

If the module tests good (or if it doesn't for that matter), make sure to clean those up real well. Also, don't forget some fresh dielectric grease where the module contacts the distributor.

 

I just had the module tested and its good. I cleaned up all the contacts, put it together and it ran pretty well for a few minutes. Now it is back to sounding like its cammin, but it's not as bad. It doesn't quite feel like its going to stall.

 

What are the mass air flow readings supposed to be?

 

I am thinking maybe this could be my egr valve sticking. Is there any way to take it off without taking the runners and fuel rail off?

 

all that has to come out to get to the egr valve is the plenum..

 

Can I clean it with it on the manifold or no?

 

You'll have to unbolt it to clean it.

 

Installed a new EGR, still idles bad

 

Glad you said that. I've just had the intake apart twice recently. Once when I reinstalled my Edelbrock runners and a couple of months later when I installed my #30 injectors. I don't want to have to do it again for a while!!!! My problem started before the injector change so thats not the problem. I'll do the IAC adjustment tonight and see if it helps my problem.....

Everything is hooked up correctly and no vacuum leaks. I even checked it with a stethoscope.... The only changes made even remotely close to the time of the malfunction was the installation of a 7.25" Fluidamper in replaement of a 6.25 Fluidamper. This seemed to make the engine run smoother with the heavy pistons that I was forced to use due to budget restraints the last time I rebuilt the engine. (6K miles ago)

Last time the cap, rotor, plugs, wires were replaced (6K ago) everything under the cap looked great. The Module is a Mallory unit that I installed circa 1997.....