Low, loppy idle then too high, then low again....

Fox Body · 07-31-2003, 12:36 PM

Hey, the GT is not doing bad, but the it's having a little problem.

1) When I first crank it after it's been sitting for overnight, it really wants to shut off if I allow it to.

2) After it has warmed up, it doesn't idle well. It'll idle high (~1100 rpm) for a few seconds, then idle low (~ 600) in a loppy kinda way (like a umh, umh umh, instead of a smooth ummmmmmh).

3) Also, if I'm driving down the road and come to a light it'll idle high like mentioned in 2), then low, then high... even when I'm driving and am slowing down for a stoplight, if I depress the clutch pedal, it idles high (above 1000) and then after I FINALLY come to a dead stop, it'll drop down, but hten go up then down , etc (as already mentioned)

Just to start off with easy things that I know haven't been recently changed anyway, I put in a new fuel filter and spark plug wires (trying to start off with the easy stuff).

Could I be losing vacuum somewhere? What is the hose that comes out from the inside of the cavern of the upper intake (directly above the lower intake)? There are 2 hoses. The smaller one on the left (if you are looking at the intake from the front of the car) seems to be old and almost corroded. From the intake, I think it goes to a plastic junction that then goes to that smog canister. It's not easy to get to that's why I haven't changed it yet.

Any ideas guys??? I don't really care for a ruff idling car........

RDRZ · 07-31-2003, 01:47 PM

I have a '81 Toyota truck (it's my wheeler) and I had the same problem that you have. My problem was a vacuum line totally fell off of the carb. I can't remember exactly where it was connected to, and I am at work right now, but when I get home tonight I will try to figure out exactly where it was. I don't know if this will help you other than it is a good possibility that it is a vacuum leak (hopefully). Take a piece of vacuum hose and listen through it at different places on your motor to see if you can hear anything.

VeNuM · 07-31-2003, 03:01 PM

Sounds like a vacuum leak to me, also could be your TPS.

88fivepointoh · 07-31-2003, 03:43 PM

did you disconnect your battery at all recently. you could just have to reset your idle. hope that helps!

Roket · 08-01-2003, 04:51 PM

I took carb cleaner and sprayed the intake and found a leak....my car does the same exactly thing. and it was the gasket between the upper and lower intake.

Fox Body · 08-04-2003, 06:20 PM

Thanks for your input (sorry took me so long to reply, my internet's been off and on this week).

Yes, this does seem like a vacuum problem. If it were the '79, it'd be easy to figure out, but you can never right off tell with these newer cars....

I'm gonna change out that emissions hose coming from the intake cause whether that is specifically the problem or not, looks like it'll be a problem soon. I'll see what happens. If that does not do it, then we'll talk.

I have disconnected the battery recently, but this problems seems to be different than just a idle (to high or too low) problem.

Thanks.

Fox Body · 08-05-2003, 11:29 PM

Well, that emissions hose was the problem. I changed it out and another piece and the car runs perfectly now. It was worse than I thought it was... just about completely dry rotted. I love an easy fix.

07-31-2003, 12:36 PM	#1
Fox Body Mustang Maniac Join Date: Sep 2000 Location: GA, U.S.A Posts: 2,266	Low, loppy idle then too high, then low again.... Hey, the GT is not doing bad, but the it's having a little problem. 1) When I first crank it after it's been sitting for overnight, it really wants to shut off if I allow it to. 2) After it has warmed up, it doesn't idle well. It'll idle high (~1100 rpm) for a few seconds, then idle low (~ 600) in a loppy kinda way (like a umh, umh umh, instead of a smooth ummmmmmh). 3) Also, if I'm driving down the road and come to a light it'll idle high like mentioned in 2), then low, then high... even when I'm driving and am slowing down for a stoplight, if I depress the clutch pedal, it idles high (above 1000) and then after I FINALLY come to a dead stop, it'll drop down, but hten go up then down , etc (as already mentioned) Just to start off with easy things that I know haven't been recently changed anyway, I put in a new fuel filter and spark plug wires (trying to start off with the easy stuff). Could I be losing vacuum somewhere? What is the hose that comes out from the inside of the cavern of the upper intake (directly above the lower intake)? There are 2 hoses. The smaller one on the left (if you are looking at the intake from the front of the car) seems to be old and almost corroded. From the intake, I think it goes to a plastic junction that then goes to that smog canister. It's not easy to get to that's why I haven't changed it yet. Any ideas guys??? I don't really care for a ruff idling car........ __________________ 351W-powered 1979 Ford Mustang Ghia notchback '79 Video @ Idle Stock 5.8L under 4" cowl 'glass hood, C4 w/ Transgo shift kit, Holley 750 cfm, Edelbrock Performer RPM intake; Fluidyne Al radiator, Flexalite 175 electric fan, 1 5/8" MAC shorty headers, FRPP Al driveshaft; S&W 6-point cage; 2.5" Off road H-pipe, 2-chamber Flowmasters, 8.8" Rear w/ 3.55s; Weld wheels (15x6;15x8), Front: 225/60/15, Rear: 275/50/15 Nitto NT 555R Drag Radials; 14 x 4” K&N X-stream air filter. '92 GT (5-speed) Small In Car Video Stock 5.0L, 2-chamber Flowmasters, MAC CAI, Tri-Ax, Al pedals... "Red, thou art my companion. Hasten now your quickened metamorphosis to Green that I may conquer all who dare abide there beside me. May they be left thither behind burnt black." ---Fox Body

07-31-2003, 03:01 PM	#3
VeNuM Registered Member Join Date: Apr 2002 Location: Downers Grove, IL Posts: 464	Sounds like a vacuum leak to me, also could be your TPS. __________________ 1989 Black Mustang GT Hatchback, Underdrive Pulles, Electric Fan, Cold Air Intake, Headers, Offroad H-Pipe, Magnaflow catback, Steeda Tri-Ax, Fluidyne Aluminum Radiator, Timing at 14*, 3.73's Coming not so soon: 408w Ricer Hater's Club Member #59

08-04-2003, 06:20 PM	#6
Fox Body Mustang Maniac Join Date: Sep 2000 Location: GA, U.S.A Posts: 2,266	Thanks for your input (sorry took me so long to reply, my internet's been off and on this week). Yes, this does seem like a vacuum problem. If it were the '79, it'd be easy to figure out, but you can never right off tell with these newer cars.... I'm gonna change out that emissions hose coming from the intake cause whether that is specifically the problem or not, looks like it'll be a problem soon. I'll see what happens. If that does not do it, then we'll talk. I have disconnected the battery recently, but this problems seems to be different than just a idle (to high or too low) problem. Thanks. __________________ 351W-powered 1979 Ford Mustang Ghia notchback '79 Video @ Idle Stock 5.8L under 4" cowl 'glass hood, C4 w/ Transgo shift kit, Holley 750 cfm, Edelbrock Performer RPM intake; Fluidyne Al radiator, Flexalite 175 electric fan, 1 5/8" MAC shorty headers, FRPP Al driveshaft; S&W 6-point cage; 2.5" Off road H-pipe, 2-chamber Flowmasters, 8.8" Rear w/ 3.55s; Weld wheels (15x6;15x8), Front: 225/60/15, Rear: 275/50/15 Nitto NT 555R Drag Radials; 14 x 4” K&N X-stream air filter. '92 GT (5-speed) Small In Car Video Stock 5.0L, 2-chamber Flowmasters, MAC CAI, Tri-Ax, Al pedals... "Red, thou art my companion. Hasten now your quickened metamorphosis to Green that I may conquer all who dare abide there beside me. May they be left thither behind burnt black." ---Fox Body

08-05-2003, 11:29 PM	#7
Fox Body Mustang Maniac Join Date: Sep 2000 Location: GA, U.S.A Posts: 2,266	Well, that emissions hose was the problem. I changed it out and another piece and the car runs perfectly now. It was worse than I thought it was... just about completely dry rotted. I love an easy fix. __________________ 351W-powered 1979 Ford Mustang Ghia notchback '79 Video @ Idle Stock 5.8L under 4" cowl 'glass hood, C4 w/ Transgo shift kit, Holley 750 cfm, Edelbrock Performer RPM intake; Fluidyne Al radiator, Flexalite 175 electric fan, 1 5/8" MAC shorty headers, FRPP Al driveshaft; S&W 6-point cage; 2.5" Off road H-pipe, 2-chamber Flowmasters, 8.8" Rear w/ 3.55s; Weld wheels (15x6;15x8), Front: 225/60/15, Rear: 275/50/15 Nitto NT 555R Drag Radials; 14 x 4” K&N X-stream air filter. '92 GT (5-speed) Small In Car Video Stock 5.0L, 2-chamber Flowmasters, MAC CAI, Tri-Ax, Al pedals... "Red, thou art my companion. Hasten now your quickened metamorphosis to Green that I may conquer all who dare abide there beside me. May they be left thither behind burnt black." ---Fox Body

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07-31-2003, 01:47 PM	#2
RDRZ Registered Member Join Date: Aug 2001 Location: Citrus Heights, CA Posts: 74	I have a '81 Toyota truck (it's my wheeler) and I had the same problem that you have. My problem was a vacuum line totally fell off of the carb. I can't remember exactly where it was connected to, and I am at work right now, but when I get home tonight I will try to figure out exactly where it was. I don't know if this will help you other than it is a good possibility that it is a vacuum leak (hopefully). Take a piece of vacuum hose and listen through it at different places on your motor to see if you can hear anything.

07-31-2003, 03:43 PM	#4
88fivepointoh Registered Member Join Date: Aug 2002 Location: Rochester Posts: 553	did you disconnect your battery at all recently. you could just have to reset your idle. hope that helps!

08-01-2003, 04:51 PM	#5
Roket Registered Member Join Date: May 2002 Location: Ottawa illinois Posts: 41	I took carb cleaner and sprayed the intake and found a leak....my car does the same exactly thing. and it was the gasket between the upper and lower intake.