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Old 12-04-2001, 11:47 PM   #1
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Location: Monticello,KY,USA
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Car: 86 IROC
Engine: 305 TPI
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rough idle

I have had problems with trying to get my car to idle correctly. When it is cold idles really rough ond dies if you don't keep giving it gas. After it warms up alittle it won't die, but it still idles rough. I have changed the evap canister and checked the canister purge valve, but that didn't help any. I also took the tb off and cleaned it thoroughly. That didn't help either. If i disconnect the vacume line that runs from the canister purge valve to the tb the the car idles and runs fine, but I don't want to leave it this way, because pressure stays built up in the fuel tank. I am also not getting any codes from the ecm.

Any suggestions?

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86 iroc, tpi, auto, compucam, headers, pace-setter cat-back, stageII chip, afpr, air foil, filters, maf screens removed, gutted air cleaner box, 160* stat.
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Old 12-05-2001, 02:10 PM   #2
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Might be time for plugs/cap/rotor, maybe even plug wires.
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Old 12-05-2001, 03:48 PM   #3
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Location: Doghouse ииииииииииииииииииииииииииииииииииииии Car: 1989 Formula 350 Vert Engine: 350 L98 Transmission: 700R4 Axle/Gears: B&W 3.27
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Car: 87 Formula T-Top, 87 Formula HT
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It depends on what you mean by "rough" I had a similar problem, it was the temperature sensor for the ECM on the front of the intake base.

The car would start, idle high then die, each time I started her it would run a little longer until it got a really unstable idle, up & down, Up & down, eventually it would idle ok. Replaced the temp sensor & it fixed everything.

John

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Old 12-05-2001, 04:52 PM   #4
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The plugs, rotor, cap, amd wires are all fairly new.

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86 iroc, tpi, auto, compucam, headers, pace-setter cat-back, stageII chip, afpr, air foil, filters, maf screens removed, gutted air cleaner box, 160* stat.
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Old 12-05-2001, 09:33 PM   #5
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Ya know, we could keep guessing at things to do...and you could keep coming back and telling us that you've already done them, and then we could guess at more things to do...then you could reply back that they've already been done...see where I'm going with this? Click the image to open in full size.

Or, you could list the problem and all recent work you've done to try and correct it.

From what I gather above in your first post, you're creating a vacuum leak and probably a higher idle...both of which would "mask over" a miss-fire at idle to some degree.

So how about we start off with some pertinent information?

What the idle RPM's at?

Does it miss at cruise/part throttle?

What led you to unplug the vacuum line in the first place? I assume you either think the EVAP hassome issue (explain why) or you may have been poking around with the engine running, pulled the line for the heck of it and noticed a better idle.

Have you pulled individual plug wires to narrow it to a cylinder? Pulled injector clips to narrow it?

What we'd like to do is narrow the problem down to either an ignition problem or injector problem assuming all other variables are okay (valves , idle speed,etc..i/e if it's idling at 500rpms, could be the reason you feel/hear a miss/rough idle)
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Old 12-05-2001, 11:19 PM   #6
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The engine has less than 14,000 miles on it. That includes the heads and fuel injectors. The coil, cap, rotor, plugs, and wires have less than 2000 miles on them. The reason why I had the vacum line off, was when I cleaned the tb, I forgot to hook it back up. Upon restarting the engine after cleaning the tb, I noticed that the vacum line wasn't hooked up. It ran fine while the vacum line was unhooked, but when I reconnected the line, it started idleing rough again. That is how I Know it runs fine while the line is unhooked.

It ran great up until about a month ago and within the span of about a week, it developed this problem.

I have good fuel pressure at idle; 42 psi. I have tried adjusting the idle; that didn't help. None of the plug wires are touching the headers. I have tried adjusting the tps. I clear the ecm every time I try something new. Nothing so far seems to help.

The problem is only at idle (all engine temperatures)and cruising, at less than about 1500 rpm's. After it reaches a higher engine speed it runs fine. The engine idles at 750 rpm.

The evap canister has been replaced. So I don't think that is the problem. The vacum line that goes to the tb only opens the purge valves associated with the canister, it does'nt actually suck air or fuel vapors from the canister. It is a very small hose and only goes from the canister, to the tb, and to the egr solenoid.

I have tried everything that I can think of.

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86 iroc, tpi, auto, compucam, headers, pace-setter cat-back, stageII chip, afpr, air foil, filters, maf screens removed, gutted air cleaner box, 160* stat.
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Old 12-06-2001, 11:09 AM   #7
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Quote:
<font face="Verdana, Arial" size="2">
The vacum line that goes to the tb only opens the purge valves associated with the canister, it does'nt actually suck air or fuel vapors from the canister. It is a very small hose and only goes from the canister, to the tb, and to the egr solenoid.

[/b]</font>
So the line you removed does not have vacuum on it at idle? It's not the hard plastic formed line from the TB to the cannister? I wonder if you're getting some EGR at idle?

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Old 12-06-2001, 01:18 PM   #8
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It does have vacum at idle. But as far as i can tell, its only function is to open the canister purge valves and provide vacum to open the egr when the ecm triggers the egr solenoid. It shouldn't affect the way the car runs, but it does. I don't think the problem has anything to do with this vacum line but I'm not sure. When the vacum line is disconnected, more air gets into the tb, which make the engine run better, but it doesn't seem to have as much power.

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86 iroc, tpi, auto, compucam, headers, pace-setter cat-back, stageII chip, afpr, air foil, filters, maf screens removed, gutted air cleaner box, 160* stat.
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Old 12-09-2001, 03:20 PM   #9
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I am having a similar problem with my 89 TPI Formula 350. I keep getting the EGR code. Have you tried the EGR valve itself? I replaced mine and it didn't solve my problem but we didn't replace the EGR sending unit so I think that that might be my problem. If that vaccum line runs to your EGR valve and the valve is bad you would be getting some EGR and would cause the rough idle. Hope it helps!
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Old 12-09-2001, 03:52 PM   #10
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I have not seen the Idle Air Control Valve mentioned yet. (IAC) If the problem is only at idle and below 1500, then I would make sure it is functioning correctly. Especially when a vacume leak allows it to idle smoothly.
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Old 12-10-2001, 11:45 AM   #11
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Do you have access to a scanner? If so, check, in addition to the great advice already given, your MANIFOLD AIR TEMPERATURE. I had a similar problem to your's that turned out to be the MAT. Cost $6.31 at the dealer and about a half hour to swap (its under the plenum back by the distributor, must remove plenum to get to). You will see this problem on the scanner (but no codes) by watching your startup manifold air temp. Mine was showing 176* on a cold morning.........

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Old 12-10-2001, 11:45 AM
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