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Discussion Starter · #1 ·
I posted here awhile back about my 89 RC, 318 auto 4x4, TBI. It ran fine, but at idle it would stumble or stutter kinda like it would if you have a vacume leak. At that time I had already replaced the injectors and the fuel presure regulator, O2 sensor, thermal stat. Since then I replaced the temp sensor as advised, which did help out on the over heating a little, but it still had a stutter. This weekend I replaced the MAP sensor and the TPS sensor which did nothing for improvement, still stutters. I got a vacume pump with a gauge and it's pulling about 22 on the vacume at idle( it's bounces between 22-23 with the stutter ). Is this normal vacume at 20+? I got the vacume pump with the gauge to try and find any vacume leaks with any of the lines, which I found a big fat 0. The timing is at 10* BTC. The idle is a little high I think ( I would guess about 800-900 RPM instead of the normal 650 RPM ), might this be a problem? The idle actuator is working, I can hear it when I turn the key on or off.
Question's
#1 Normal vacume 20+?
#2 Could high idle be causing this stutter ?
#3 Any other ideas as to cause ? Maybe a gasket ?
 

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Jeez... what else could it be...
The only other "simple" things I can think of are the PCV valve and EGR, where a malfunction could maybe cause the vacuum to fluctuate... altho it would be good to set the idle at spec... 800 rpm (or whatever your Emissions Sticker says is the correct idle speed).

I may have missed some of the earlier discussion; so, what does your "stumble/stutter" sound like:
A short cycle -say one second or so- mMmMmMmMmM...?

Or long cycle of several seconds up several down- mmmmMMMMmmmmMMMMmmmmMMMM...?

OF unequal length, or relatively regular- mmmmmmMmmmmMMMMMMmmMMMMMMMmmm ?

The vacuum sounds pretty good... but it oughta be about 16 at idle,
Does your have a "vacuum transducer" on the computer? If so, it could be reading the vacuum fluctuation and changing the timing slightly, which might cause the idle speed fluctuation...

But that doesn't explain the vacuum fluctuation...

Does the "Automatic Idle Speed" motor (see a manual for the explanation of the test procedure) work ?

I certainly hope that it's not a slightly sticking or slightly burnt valve...

Have you gone down the line, pulling one plug wire at a time to see what effect that has on the idle?
 

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Discussion Starter · #3 ·
It's an intermitant stumble so to speak. If I go to the tail pipe, I can hear it, and I can feel it inside the vehicle. If it was a regular stutter, I'd be able to track it down with no problem. But, being an illregular one, I'm about to pull what's left of my hair out just trying to figure it out. I did change out the EGR valve and the PCV valve before trying to figure this out.
Like today, it ran fine, the idle was normal and no stumble or vibration. Nice and smooth like I think it should be. I live I Phoenix, AZ, the weather is mostly sunny and the air is dry. I rained yesterday and today, so the humidity was up a bit. It's weird, whenever the humidity is up, it sometimes runs preaty good. Ooh yea, the sticker under the hood says the idle should be at 650 RPM.
I forgot to mension that my mileage is a little better than 11 on the freeway, and about 10 or so in town. Where before, I was getting around 16 in town or on the freeway.
 

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could it be running a bit lean @ idle? Thinking it might be just lean enough to the point a little thicker air (humid) might cut down the air flow a tad and let it smooth out a bit. Does it di it when it warm, cold, always?
 

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Well, since you got the vacuum pump, did you hook it up to the ECU (to see if steady vacuum changed anything) and run it.

Humidity equals higher density air, higher density air burns better, not worse...

Lower fuel mileage means more fuel is going somewhere...

When did you last replace the plug wires, and when did you last do the "one at a time test".
 

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duh! Sorry Smokey! lol
 

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Discussion Starter · #8 ·
I'll try hooking the vac. pump to the map sensor tomarrow when I get home. I pulled the plugs today and they all look like a light cinimon, which is good. I changed the plugs and wires back in November.
 

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I think I would try a can of Seafoam and run it through the fuel system. www.seafoamsales.com and I would also take a look at this service bulletin http://dodgeram.info/tsb/1989/14-02-89.htm
Could be that your fuel pump or intank filter is about to take a dump on you? Maybe a small hole in a fuel line?
 

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Another thing you might want to try is the EGR transducer (at least that is what a parts guy here called it). It is a little black spaceship looking piece that sits near the EGR, towards the front of the vehicle. There is a short hose connecting it to the EGR, and the other part of the tee on top goes to a vaccuum source. The bottom of the transducer has a hose fitting as well.
Inside of this part is an orange diaphragm, and if it has even a small tear in it, you will get a stutter at off-idle. I could not even park properly nose-to-nose with another vehicle because of the stutter. The bad news is that to get a new one, you have to get it AND a new EGR from, you guessed it, the dealership. Yes, I have a 1990 R/C, and you have to get it at the dealer....or the scrapyard.
You can carefully pry it open with a medium sized flat screwdriver and see if the diaphragm is intact. If not, go to your scrapyard and start pulling and prying till you find one that is in good shape. You will have to clean up some carbon, but it has eliminated the problem in mine.
 

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If the Egr was/is causing a problem, you could just disconnect the egr solenoid located on the passenger side valve cover. should be three solenoids there, not sure which one is egr, but that would eliminate any vacuum from reaching the egr valve. Also, you might want to spray some carb cleaner or other similar fluid around the intake and various vacuum hoses. I did this recently with brake cleaner, and discovered a leak around the tbi mounting gasket.
C.J.
 

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another thing may be that the rotor bushing inside the distributor is worn, and is letting the rotor wobble just a little bit. every now and then it will get just far enough off to cause a miss which would be a stutter. mine does the same thing, it just hasn't bothered me enough to fix it.

Jake

 
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