The lowest number is 13, which might indicate that my IAC is having some issues. I've tested it as best I can and it seems to check out OK.

The next is 34, which my book says is caused by "RPM did not drop when EGR valve was opened." I replaced a faulty EGR position sensor but the code remains.

Next up would be the 41 the "always lean" condition the oxygen sensor seems to be reporting.

Could an idle or EGR problem really be causing these problems? It almost has to be a fuel or ignition type problem I'm dealing with here doesn't it?

 

Do any of these codes occur in CM (Contineous Memory)????

You should begin with code 13 & find & fix that problem first.

My manual shows 3 possibilities, depending on when the code is pulled. All appear to have to do with the D.C. motor not moving, or not following the dash pot, such that the computer thinks it can't control engine rpm during the low rpm test!!!!

Then address code 34, which my manual says can be several things (4), depending on when it's pulled, but most of them deal with the EVP ( EGR Valve Position sensor) or it's signal circuit.

In any case the computer isn't happy with what it's being told about the control of the EGR valve, via the EVP sensor or it's circuit.

On the code 41, I show two meanings, depending on where the code is pulled.
One is as you read it, system lean.
The other, if this code is also in CM, (Contineous Memory), No EGO sensor switching detected!!!! Which if true, would suggest the O2 is not working, or it's circuit is open, like maybe a defective electrical connector, or broken wire.

So has the O2 sensor ever been replaced???? If so how many miles on the O2 sensor????

Also, if the EGR's operation is being messed up, or it or it's vacuum circuit has a vacuum leak, it could mess with the Air/Fuel mixture & drive the 02 sensor & computer, nuts!!!!

Just some more ideas for consideration.

Let us know how you do.

 

The codes only occur during the KOER test. KOEO and CM both give a code 11.

As for the O2 sensor, it is the original I believe. Which would mean it has about 18 years and 134k miles on it. Might be time to replace that one.

As far as the other two, I replaced a faulty EVP but that didn't make the code go away. I think the signal voltage to the plug is ok. Also as far as I can tell the IAC is ok.

Things are tight right now and I have some trepidation sinking money into parts that aren't directly related to this exhaust popping and the resultant poor engine performance. I know that the EGR system has a problem that needs fixing, but would it really affect the engine at idle? I thought that part of the system was only supposed to be operational during highway cruising speeds after the engine is warm.

 

Ok good CM feedback, that helps narrow down the list meanings some.

So now the code 13 is "Can't control RPM during low RPM test.
So you need to find out why it thinks it can't move the throttle then.

Code 34 is EVP voltage out of range during self test.

To answer your question about whether the EGR will affect idle, it'll all depend on whats wrong with the EGR system.

If it's operating at the wrong time or leaking vacuum, it'll mess up the air to fuel ratio. So you need to confirm if the EVP sensor signal voltage is present & at the correct value & it's output to the computer is getting there. No open circuits, intermittent loose or dirty pin/socket connections at the EVP sensor or computer.

Code 41 as you read it, EGO sensor indicates system lean.
As we've said before, if you have a up stream vacuum leak, it can cause this, or it could just be an old, tird, lazy O2 sensor.
Could be that EGR problem too. Thats why you need to clear that code first.

On the O2 sensor, most folks change them between 75 & 100K miles. It is possible for them to work, but be lazy, slow to respond.

Would be nice if you could get a scan tool on the truck, to monitor it & watch it's output & see if it's switching as it's supposed to.

Just keep hacking away at the problems. Work the lowest numbers first.

 

I can't find any vacuum leaks and I can't seem to fix this problem or make the codes go away. As best I could test the EVR, the DPFE and EGR seem ok. I tested for vacuum from the EGR's vac line and got nothing and the book said it should be less than 1. The valve appears closed, and trying to open it by applying vacuum doesn't make any difference in engine performance. The computer is picking up the signal from the EVR. The code 34 remains.

As for the 13 I tried to fix that with a new IAC but it didn't do any good.

The vacuum is still bouncing between 1 inch, between about 17 1/2 and 18 1/2. My truck was idling pretty decent this evening so I decided to try a little test drive. As soon as I tried to back out of the driveway it promply sputtered and died.

I really appreciate everyones help so far, I hope we can figure this out.

 

Disconnect and plug all the vacuum taps on the intake manifold to make sure that you don't have an 'extra' unknown leak somewhere, like under the dash, etc, that is allowing extra air.
The EGR will not get vacuum until the engine is warm, and a specific rpm is reached. It waits until warm for driveability, and then applies vacum to the diaphragm on an as needed basis. IF you apply vacuum at idle, the engine should sputter and perhaps die. If you don't get that response, the EGR may be inop or the tube from the exhaust plugged.
If your idle is set on the 'hard stop' at a too high rpm, then the ECM will complain that it can't control the idle speed. It tests by raising and dropping the idle speed during the KOER tests. If it is too high, it thinks that it could not get a good response. The hard idle should be less than 750 rpm, I think.
If your vacuum reading is bopping around, look at the instructions or a chiltons/motors manual for what the vacuum needle fluctuations mean. I have heard of 2.3 engines having valve springs that got weak. cause it to run weak at anything above an idle. Good compression, etc, but the valves just couldn't keep up... tom

 

According to what I can gather, a vacuum fluctuation like that could indicate an ignition problem. I'm also suspecting that too much gas is being used. I'll try your suggestion of plugging all the vacuum fittings on the intake.

As for the EGR I was perplexed that applying vacuum didn't affect engine performance, perhaps it is stuck or something. It looks to be closed, so if it is stuck closed it shouldn't be affecting performance anyhow. If it were leaking exhaust into the intake at the wrong time would this cause the popping and severe power loss?

I do not think that I can adjust the idle on this truck. I hope I don't have a valve issue, the motor only has a few years and 34k miles on it. But anything is possible. I guess I'll head on home and mess with it some more, thanks for the ideas.

 

I agree with tomw, if you applied vacuum to the EGR valve & the idle didn't change, it would suggest something is wrong in the EGR circuit, like an inoperative EGR valve (maybe a ruptured diaphragm a good vacuum leak source), or plugged up pipe, coming from the exhaust manafold, or going into the intake manafold.

Your code 34, is saying something is amiss there also. So pull the EGR valve & make sure it's functional, by applying vacuum to it & watching it open & it's inlet & outlet pipes are clean, ALL the way through!!!!!

On the code 13, test the DC motor, or solenoid, or whatever the computer uses to move the throttle for idle adjustment, & make sure it's functioning ok electrically.

 

I pulled off the EGR valve (it was a real pain) and it looks like it is stuck open a bit. When I apply vacuum to it the valve doesn't seem to want to move. So I guess I have another part to replace.

 

OK, thats a good find!!!!
Does it seem to be leaking vacuum????

How do the connecting pipes, from the exhaust manafold & into the intake manafold look for deposits????

 

No it does not leak vacuum, and it doesn't seem to move when vacuum is applied. Any idea about how far the end of the valve stem is supposed to be recessed into the hole that connects to the exhaust pipe? on mine it seems to be resessed about a quarter to third of an inch.

The pipe and the intake inlet seemed fine, no blockage. The intake port did seem to have a coating of kind of wet black stuff inside.

 

Someone else will have to offer up inputs on how your particular vintage EGR valve should look & respond.

You could try cleaning it with a good spray solvent cleaner, formulated for cleaning carbon & RGR valves & see if it frees up.

Just be careful NOT to get any into the EGR valves vacuum port, as the solvents may get after it's diaphragm.

Does the wet/black coating feel oiley????
Is it in the pipe coming FROM the exhaust manafold, or is it in the pipe going INTO the intake manafold????

 

I've tried spraying out the EGR and plan to let it sit with some solvent in it overnight.

The black coating, inside the port on the intake manifold from the EGR valve did feel a little oily, or at least moist.

 

Slanta ,
Have you tried listening for a vacume leak . I know they can be hard to pick up over the "din " . I am intrested in the RPM at Idle , is there a Great fluctuation ?
Detret

 

No vacuum leaks that I have been able to determine. I fixed one at the brake booster, but it didn't solve the problem. Idle is pretty normal, except for the popping noises in the exhaust.

I've tried to clean the EGR valve to free it up but have been unsuccessful so far. I'd just replace it since it is bad, but just can't afford it right now. I'm not even too confident that it is the problem. I sure do miss my truck, hopefully we'll figure this out one of these days.