Suburban running rough

[Burbdood 74]

Time for an update......

it's still surging at idle and when you put it in gear, it stalls out every now and then and still no codes to speak of. To date, I've replaced the CTS and the O2 sensor, the EGR solenoid, put in a new fuel pump and replaced my bad injectors. My heart tells me it's either a vacuum leak or the EGR valve but the EGR doesn't leak and I've cleaned it twice.

I can't find any vacuum leaks to speak of either. One thing though, when I take the vacuum line off of the MAP sensor and plug the line, it smoothes right out. Could my MAP sensor be bad?

Please please please help me out here.....

 

[Fordum]

Well, just run it without the MAP sensor..........

Actually, sounds like you have a leak in the MAP sensor.

 

[4xcrazy]

I doubt it, not saying it's not possible to be bad, I replaced a good MAP sensor because mine did the same thing when I took the vac hose off trying to troubleshoot an issue. Mine ended up being a split hose on the fuel pump, that litttle 2" hose from the pump to the sending unit.
But you said you replaced the pump, so unless you reused the original hose, it's obviously something else.

 

[nutt7]

Possibly the fuel filter? Usually idle is ok with a bad filter, but it could account for some stumbling upon acceleration...

 

[Burbdood 74]

I changed the fuel filter two weeks ago along with the fuel pump.

I just checked to see if there were any trouble codes and it just gave me a code 42, Electronic Spark Timing. Whats weird is that my SES light never came on for this and I replaced that a year ago.


It's hunting bad for an idle now.....high...low...high...low...and running pretty rich. If it is the EST, could my distributor be bad causing the EST to shorten it's life span?

 

[Cornfield creations]

I have seen coolant temp sensor cause poor running. Strange as it may sound, they use that signal in a lot of calculations in the computer.

 

[Burbdood 74]

I have seen coolant temp sensor cause poor running. Strange as it may sound, they use that signal in a lot of calculations in the computer.

I've seen some crazy shat from a coolant temp sensor as well on my old 90 Blazer. But I changed the CTS earlier this week with no change in idle, or lack of an idle.


So, to date I've:

looked for and haven't found any vacuum leaks
changed the fuel pump, fuel injectors and fuel filter
new coolant temp sensor, O2 sensor and EGR solenoid
taken off and cleaned my EGR valve and threw on a spare I had
threw on a spare MAP sensor I had lying around, no change
and I even threw on a spare ESC module I had with no change, so I switched it back to the old one

I've checked my timing with the tan/black wire disconnected and it holds steady where I set it 2 years ago at 4* at idle. And last night for the first time I got a code 42,(electronic spark timing).

 

[ccarley]

I've had a code 42 in the past as well. When it got triggered, the idle dropped way low, and it hunted for a good idle.

I believe it's a loose connection somewhere in my '89

The Chilton's manual suggests that if you have that code currently, and it runs, then the tan/black wire is disconnected somewhere. If you have that code and it does not run, then the wire is grounded. Disconnecting that wire to check timing will set that code.

Have you tried disconnecting the battery for 20 minutes, let it run for a while & see if any codes come up? Not that it will fix the problem, but it should tell you if you still have code 42.

Now, the Haynes manual I have says if you have code 42, it's either that wire, or the HEI module. I'm not sure I believe that manual too much.

Good luck... I'm afraid I'm not too much help.
Clay