maxjivi05

Okay, I got this car off someone a few days ago which I had to fix a cooling problem which is solved now... Made my own air dam and needed a lower rad hose...

Okay, when I start it up in the morning "Cold Start" it starts easy, I can stop and go stop and go no problems, once the car is warmed up if I stop at a light I have to hold both Gas & Break to make the car not Stall out! This is irritating and I can't keep doing that.

I don't get paid to start swaping everything out till next week but would like to pin point out the most likely problems.

1991 Camaro RS with a EFI with a 350.
I done replaced Cap, Button, Pick-up & Ignition Coil.
I will be replacing Plugs/Wires next week for sure.
TPS?
ERG Valve?
IAC? I cleaned it out it opens and closes but barely moves?

Anything else I am missing? Thanks....

KrazyFirst

Check vaccuum lines to make sure all are connected properly and no cracked. But it sounds like a lack in fuel pressure to me. Good luck!

my86bird

Yeah, what he said(Krazyfirst). When I had a similar problem with my '86 6cyl, I went through the list also. But after much debating about what to check then replace, I discovered (and there's a story here) that I had put back, but not tightened down the flexible rubber hose air intake that spans the distance between the radiator and the tbi. Apparently, since this is after the mass air flow thingy, the extra air coming in was not being sensed by the tbi and screwing up readings by the electronic control module. Once I tightened the clamps, it performed fine. So, while your checking all the other thingies, make sure there's no air leak between the maf and whatever carburetion you got.

Good Luck!!

ASE doc

I assume this is TBI car. The 350 wasn't offered in the RS so it must be a transplant and I'm assuming they used the same TBI from the 305. It's possible that you are suffering a heat related injector failure. It could also be the IAC, the MAP, the TPS, or even the ECT sensor. How does the engine run aside from the stalling issue. Does it have good power? If so, then your trouble probably isn't fuel, as in injectors or fuel pressure, related. The IAC is tricky to test. Don't expect it to move much even if you apply power to it. It is a stepper motor and it moves in a ratcheting action as each of the two coils are switched back and forth. I have seen both the IACs fail and the coil drivers in the ECM fail. Also, the system relies on a certain amount of bypass air through the throttle body itself. This is your base idle setting and needs to be set correctly for the idle control to work right. The throttle body also needs to be cleaned of any coking build up.

In situations like these, I like to use my scan tool to view data and look for anything that's off. Look at desired idle and IAC steps. Try to force the idle high by turning on accessories. Force it low by creating an air leak(disconnect a vacuum line). As you force the idle up and down, watch for idle air steps to change. Force the idle high and then disconnect the IAC and shut off the engine. Pull the IAC out of the TB and see if it is fully extended. Then, force the idle low, or just reconnect the IAC and cycle the key on and off. This should place the IAC in engine start position where it opens up to allow extra air for engine starting. Now pull the IAC out of the TB and see if it has moved to the open position. Thexton Tools makes an IAC tester that works to actually operate the IAC and quickly proves whether the stepper motor is okay or not. This saves time in determining wither it's the valve or the control circuit.

To test the control circuit, just use your DVOM to test for 12v across each coil drive circuit. The control signal to each coil should switch from positive to negative as the ECM commands the idle up or down. I like to use my lab scope for this as I've had some where the control signal turned to crap and even though there was voltage there, it wasn't moving the IAC. My scope lets me see the actual pattern.

maxjivi05

Pretty sure they got the 350 out of a Z28, it's EFI with 2 Injections on top of the Throttle Body. I disconnected the O2 Sensor to see if it made any changes and the car still surges, hunts for idle and while in gear it'll stall out if warm enough, I made my own wing to keep it from getting hot and it works great forcing air through the radiator.

The car has good power when starting out Cool, or if I let it sit for a short period of time then going. 1 More thing, the battery in this car right now is bad! I don't have the $ to buy a new one for another 1-3 days so in the mornings I have to jump the car but the alternator is good, it runs just fine, and if I try to start the car like 10-15 minutes after I shut it off it'll start right up sometimes, sometimes it don't have the juice.

When we set the time we didn't unhook the EST like I read we should a few minutes ago. I did disconnect the IAC, tested, Cleaned Hook it up and tested it, plugged up the EGR to see if it made a difference, didn't change! and I unplugged the O2 sensor and it didn't make a change, ran a little better actually when it hooked up...

There isn't away to set idle higher that I know of on this car, I had to wrap a piece of small wire around where the throttle cable pulls so it don't go all the way back so it won't stall out on me.

Any clues? After a lot of reading I am suspecting the Intake Gasket but don't have Carb cleaner to test it just yet.

ASE doc

The TB gasket leaking isn't uncommon. Intake manifold gasket on chevy is a very uncommon cause of an air leak. The 350 in the Z28 was TPI. Only the RS got TBI. Doesn't mean the long block didn't come from a Z car.

One thing that gives me pause. The battery is dropping out. Anytime that battery voltage drops below 10v, the ECM memory is reset. This means it is losing its idle strategy every time. It takes time for the ECM to learn idle strategy. We can short cut this process by performing the base idle setting procedure but the next time the battery goes dead or is disconnected, it's lost again. You need to replace the battery before you can repair the idle problem. You need to set the timing as described in the service manual. Basically, warm up the engine, shut it down, disconnect the timing connector which is inline in the tan/black EST wire, start the engine, set the timing to 10 degrees(book may say 6 or 8 but 10 is better), shut down the motor, reconnect timing connector, clear codes. Of course, all of this will be very difficult on an engine that won't idle hot.

The surging and hunting is a lean condition or the EGR stuck open. Now, when you say you plugged the EGR, do you mean that you removed the EGR valve and blocked the passages? Plugging the vacuum port won't help if the valve is stuck open. The intake is still sucking exhaust gas in. EGR valve being stuck open is a very common problem.

I have seen several TBI cars that had broken fuel pressure regulator springs inside the throttle body and had low fuel pressure because of it. They surged and hunted for idle and stalled in gear. But, they ran worse cold because a cold motor wants more fuel. That's why I don't think it's fuel pressure related. Have you checked the ECT sensor?

ASE doc

One thing I didn't even think to mention is injectors. Even the low impedance injectors in the TBI can fail and injector failure is not uncommon. Remove the air cleaner so that you can see the injectors as the engine runs. Start it cold and look at the injector spray. It should be a fairly solid cone and will touch the sides of the throttle bore on throttle snap. Now, let the engine warm up til it starts to falter and look at the injector pattern again. Is one injector not spraying? Or has the injector spray deteriorated. Checking fuel pressure might be good too because you could be dealing with a fuel pump that's dropping pressure.

maxjivi05

Okay, no I plugged the hose but I found a break in the hose repaired it and still surges, and fails to idle... I am going to get a Battery possibly today.

I did find last night when My car is warm if I disconnected the coolant temp sensor it'll idle easier sometimes.... but when I plugged it up it stalled while in gear... It could of been because of the electric flow taking more power from the Bat ... but I don't know... This morning it drove to work and stalled with it disconnected but either way I'm going to replace bat today, possibly the coolant sensor, and egr valve with new lines...

I don't see no Vacuum from the EGR Valve? How do I know it's working properly?
I pulled the plug and tried to see if any suction was going on and had None.

ASE doc

The EGR is opened by ported vacuum from the throttle body. Ported vacuum means that there is only vacuum when the throttle is open, not at idle. The EGR valve cannot be open at idle or it will cause the engine to run just like yours is running now. The purpose of the EGR(exhaust gas recirculation) valve is to inject a metered amount of exhaust gas, which is almost pure CO2, inert gas into the intake air stream. The inert gas cools the combustion temperatures by diluting the intake charge. This helps to lower the production of Oxides of Nitrogen which is considered by the EPA to be a noxious pollutant gas.

Because these emissions compliant cars(1976- on) also tend to run very lean, the reduction of combustion temperatures produced by the EGR system also helps prevent valve damage, which might otherwise occur. Valve damage is more of a risk when low octane fuel is used and/or in high ambient temperatures. Therefore, it is recommended by me and most other experts that the EGR valve not be deleted or decommissioned on otherwise stock engines.

If you have installed aftermarket cylinder heads, cam, and headers, and tuned the ECM for these modifications, you may be able to delete the EGR without any negative effects. Otherwise, it is best to keep it working. If the EGR valve has failed, you may try blocking off the passages with a block off plate and running without it. Just be aware of your engine and listen for any detonation(pinging). If you hear pinging, you will need to address it by either running higher octane fuel, retarding timing, or replacing the EGR valve, or all of the above.

To determine if the EGR valve is stuck open, you can try using your fingers below the diaphram to lift the pintle. If the pintle seems to be stuck in the raised position, you must remove the valve from the intake manifold and look for the pintle to be raised off its seat. It is common for carbon to build up around the pintle and cause it to stick open. If this is the case, clean the valve mechanically using a small screwdriver or other tool to remove as much of the carbon as possible. Then you may also use carburetor cleaner to soften and remove any remaining deposits. Test the valve for freedom of movement by opening it with your fingers and allowing it to close. Be sure it moves freely.

You can try testing it with a vacuum pump but many of these valves are pressure modulated, meaning that they will only open with vacuum AND exhaust pressure. These PM valves will bleed off vacuum very quickly and you will think that they are no good, but in fact they are working normally.

maxjivi05

Finally got some money from a phone I sold to work on the car...

Replaced Plugs / Wires and while pulling the wires I noticed whoever ran them was retarded and had them all over the heads, and exhaust etc... Needless to say while the car was hot it was burning into them causing them to ground theirself and run horrible.

Once Replaced the car ran almost like a champ, need to set the timing a little better since they are all firing correctly now, drove 60 miles no SES light but this morning on the way to work SES! 23, 32, 34, 44. High Vacuum, EGR Malfuction, TPS or Low Temp at Manifold etc... Anything to worry about? Also says "LEAN" could be from these codes or previous codes?

I didn't clear the codes by letting the battery sit unhooked, just next time I started the car they all were gone, could it just be stored and poping up?

maxjivi05

Well after driving for miles and miles.... It tosses a code "LEAN" then when I shut it off and turn it on it'll stall... I cleaned everything, ran seafoam through the system and did the tune up.... vacuum lines are all there, MAP even shows HIGH vacuum. so I don't know... Any thoughts? Runs good long as I don't change gears... drive...park... drive... Stall... or park... reverse.... STALL

maxjivi05

I unplug EST and it idles FINE... Does this mean it's a sensor of some sort? Vacuum would make it stall out even with EST unplugged?

Is it safe to drive with EST unplugged for now? I set timing with EST Unplugged and disconnected the Battery then plugged EST up and battery after it sat for a while... It just don't idle after warmed up... tosses code "LEAN" after warmed up and that's all..

ASE doc

So you never checked the EGR? Code 23 is "inlet air temp low". Look for the air temp sensor in the air cleaner to be disconnected or an open in that circuit. Code 32 is EGR fault. You need to test the EGR by lifting the diaphram with your fingers like I told you to before. Code 34 is MAP high vacuum indicated. It may be that the sensor is no good or that the signal circuit is shorted to ground or open. It may also be related to the EGR failure so get the EGR figured out first. Code 44 is O2 sensor lean exhaust indicated. This could be a bad O2 sensor but considering your other codes I bet it's probably a secondary code.

It would be easiest to diagnose this car using a scan tool to read datastream. Scan data would show you actual MAP voltage, O2 voltage and you could watch for changes as you work the EGR. Short of that, perform the EGR stall test. Simply lift the EGR diaphram at idle and the motor should stall or at least fall off like it wants to stall. If this doesn't happen, you need to remove the EGR valve like I told you before and check it for clogging or being stuck open. Also, while you have the valve out, make sure the passages in the intake manifold are clear.

maxjivi05

EGR Vavle is clean, I took it out cleaned it good and it moves freely, no issues what so ever, I don't notice vacuum at the EGR at all but that's at idle... and when I hit with the throttle outside the car nothing... Not sure why it don't do anything but I'll have to hunt it down I guess.

Just don't make sense why it would run fine with EST unplugged and not plugged

ASE doc

Yeah. That is a little odd. It is most likely an issue with the ICM. You could diagnose it with a timing light and an inline spark tester. First, verify timing with the EST disconnected, then shut down the engine. Disconnect the battery for 30 seconds to clear the ECM memory, then connect the inline spark tester and run the motor watching the spark for drop outs and also watch timing for being out of normal spec. Normal timing with EST activated will be about 16-20 degrees at idle and will shoot to 40+ on throttle snap.

The EGR is pressure modulated and it won't open unless you're driving. The vacuum to the EGR is ported. You will only see vacuum at the EGR with the throttle open and the engine cruising. The EGR solenoid is deactivated at idle and when the engine cold. When deactivated, the EGR solenoid doesn't pass vacuum to the EGR valve. There were two different valves used on the 91. On is negative back pressure the other is positive back pressure. The negative back pressure valve will only open when there is no exhaust back pressure, such as under cruise conditions. The positive pressure valve only opens when there is exhaust pressure. The final character of the part number will be a P for positive or an N for negative.

The lean indication from the O2 sensor and the MAP high vacuum tell me that there is more than just an EST issue. But the fact that the engine runs okay without EST can't be ignored.

You may need to find a scan tool. The Snap On MT2500 is available cheap on Ebay or Craigs List. Or you can get WIN ALDL. The latter is free online. You just have to make your own interface cable. The scan tool will let you see what the MAP data, O2 voltage, and commanded timing. You can also watch Integrator and Block Learn which are the fuel trims. Fuel trims tell you if the engine is running lean or rich. Watching O2 voltage will tell you if the sensor is actually functioning or if it's just stuck lean.

ASE doc

In post #7 I mentioned injectors. This does sound somewhat like a heat failure of an injector coil, something to look at. Chase down the cause of code 34. Use your DVOM to check voltage on the signal circuit. Should be about 4.5 volts with the key on, engine off and 1.6v at idle. Voltage should rise with manifold pressure so it should go high when you snap the throttle.

cfs2chvy96sub

iv just a 91 rs v8 swap ,an it stalls as u put it in to gear as it is warmed up also