Idle problem and jerking?

69fastback · 01-05-2003, 02:27 PM

The car is a 91 GT. The idle problem is that when you first start the car it will not stay running at all. You have to rev up the motor to get some heat in it before it will even stay running. Then when it does stay running it will sit there and idle at 800 for a second or two then surge up too 1700 and sit there for a second the go back down to 800 with out me pressing on the gas. It does this for a little while until it get up to about 150 dagress then it will stick to its 800rpm idle. I have heard that if the throtle body is dirty they idle bad good this be my problem or is there some thing else?

The other thing the car does is it has a jerking motion that seems like it comes form the rear. It is really werid cuz this only happens when i cruise down a road at a steady speed. When going the same speed for about a quarter mile or so the car will start to jerk until i step on the gas and then the car has no problems and just takes off. This only happens when I am going a steady speed. As long as it is under acceleration the car had no problems. When the car does start to jerk though the check engine light comes on and the oil pressure quage drops all the way down (it is factory quage) then goes back up when i step on the gas hard. Does this have anything to do with idle problem or is it different. It is an aod car with a shift kit and it shifts really nice. Any help is appricated i have no idea what to do about this.

mustanggt_50 · 01-05-2003, 03:12 PM

i had the same problem with my car when i first started it up so i replaced the Idle Air Bypass and cleaned the throttle body while i was at it. That seemed to fix the problem, so take a look into that.
As for the other prob sorry but i cant help ya there.

01-05-2003, 04:05 PM

I had the same jerking prob and all that happened and that was because i did not put the downstreamtube back to the air pump for the cats but i have no cats so i left it off and someone told me that it should be put back on. Since having an off road pipe my o2 sensors were shot and check engine light would come on and engine wont performe at low speeds, so i bought some new sensors and havent had the problem since. So if you have an off road pipe then try that and see what happens.

stang4to8 · 01-05-2003, 08:14 PM

i second that, replace those o2 sensors & reset the computer by
diconnecting the neg. bat. cable for 20 or so min. reconnect
after said time & take it for a drive for awhile so car can relearn fuel curves. i sure hope you already gave it the full tune up! anytime a car starts w/ these kinds of problems, go after the easy
stuff first like all the tune up goodies.clean the idle air bypass solenoid also.

HiFlow5 0 · 01-06-2003, 08:08 AM

Do you have any mods on the car, like a cam or anything? Your jerking problem sounds like what my car did before I got a stall converter matched to my cam. But if the oil pressure drops at the same time, sounds like you might have a more internal problem.

XR1stang · 01-06-2003, 02:29 PM

heh, I have this same problem with my 94. I have heads, cam, full exhaust, etc. and this all started shortly after I did this. I just put in a new clutch over the weekend and the jerking went away for me.

I have a 70mm BBK throttle body, but right now I'm running the stock one. The BBK had a problem with TPS voltage being WAY out of wack when I installed it. It was reading 1.35 with the original TPS, so I replaced the TPS and it came down to around 1.15 but was still high. I reinstalled the old throttle body and the TPS went down to .91 so I'm guessing something is screwy with the BBK piece somehow.

Oh, my problem could also be coming from the fact that I have no EGR at the moment.... /shrug

XR1stang

01-06-2003, 03:38 PM

Quote:

Originally posted by XR1stang
The BBK had a problem with TPS voltage being WAY out of wack when I installed it. It was reading 1.35 with the original TPS, so I replaced the TPS and it came down to around 1.15 but was still high. I reinstalled the old throttle body and the TPS went down to .91 so I'm guessing something is screwy with the BBK piece somehow.
XR1stang

XR1stang-
You don't have to replace your TPS if it's voltage is out of the normal parameters. Just remove your TPS and use a file to extend the screw holes to allow for additional room to properly adjust the TPS.

69fastback · 01-06-2003, 06:05 PM

The car has shorty headers into an off road h-pipe so that sure could be my jerking problem. They only thing is the oil pressure drops too 1989 stanger did it make your oil pressure drop too? I know the 02 sensors are not hooked up so that could be the problem. Not sure of what all mods it has i bought the car at a dealership and the guy didn't know.

Not sure what the idle air bypass silonoid is?

HiFlow5 0 · 01-07-2003, 08:15 AM

Quote:

Originally posted by 69fastback
I know the 02 sensors are not hooked up so that could be the problem.

I'd hook them up, they do sure a purpose.

Shogun · 01-08-2003, 01:29 AM

69fastback, clean your Idle Bypass Solenoid (IBS) throughly, the IBS is located on your Throttle Body facing the front of the car left side, it is postioned at a 45 degree angle in relation to your TB. It has two mounting bolts and one electrical connection. Once that is clean, remove and replace the Intake Air Temperature (IAT) sensor located on the right side of the intake (lower) behind the coolant temp sensor. This sensor may be gunked up a faultly IBS. This sensor helps to control Air Fuel ratio in open loop. Also, replace those O2 sensors, you are KILLING your performance and fuel economy by not having them present. They communicate directly with the EEC-IV during closed loop operation monitoring the amount of O2 in the exhaust which in conjuction with other sensors helps set air fuel ratio etc.. OK, getting wayyy off the subject. Try those first.

Oh, one more thing, I think the reason your having problems, I believe your EEC-IV is running in Failure Mode Effects Managment (FMEM) this occurs when you lose a sensor or one goes out of range. The computer has preset values to cover that damaged/dead sensor and your engine will operate but not to its full potential. Ok, too long I know. But to Qutoe NBC "The more you know".. Hey anyone feel free to jump in if I stated something wrong.

01-11-2003, 05:58 PM

It did drop but not low enough to worry

01-05-2003, 02:27 PM	#1
69fastback IRAQ VET Join Date: Feb 2000 Location: high desert California Posts: 1,480	Idle problem and jerking? The car is a 91 GT. The idle problem is that when you first start the car it will not stay running at all. You have to rev up the motor to get some heat in it before it will even stay running. Then when it does stay running it will sit there and idle at 800 for a second or two then surge up too 1700 and sit there for a second the go back down to 800 with out me pressing on the gas. It does this for a little while until it get up to about 150 dagress then it will stick to its 800rpm idle. I have heard that if the throtle body is dirty they idle bad good this be my problem or is there some thing else? The other thing the car does is it has a jerking motion that seems like it comes form the rear. It is really werid cuz this only happens when i cruise down a road at a steady speed. When going the same speed for about a quarter mile or so the car will start to jerk until i step on the gas and then the car has no problems and just takes off. This only happens when I am going a steady speed. As long as it is under acceleration the car had no problems. When the car does start to jerk though the check engine light comes on and the oil pressure quage drops all the way down (it is factory quage) then goes back up when i step on the gas hard. Does this have anything to do with idle problem or is it different. It is an aod car with a shift kit and it shifts really nice. Any help is appricated i have no idea what to do about this. __________________ 428 Cobra Jet SOHC 5.4 3V F-150 96 mystic cobra 91 GT

01-05-2003, 03:12 PM	#2
mustanggt_50 Registered Member Join Date: Dec 2002 Location: Ontario Canada Posts: 91	i had the same problem with my car when i first started it up so i replaced the Idle Air Bypass and cleaned the throttle body while i was at it. That seemed to fix the problem, so take a look into that. As for the other prob sorry but i cant help ya there. __________________ 87 GT T-roof (needs paint) lol, rebuilt motor and trans, AOD - stage 2 shift kit, 3.73 gears - auburn posi, Dynomax Super Turbo Cat Back, FRPP 155lph fuel pump, K&N filter - air silencer removed, subframe connectors, strut tower brace. 88 GT T-roof 1989 LX Coupe 5.0 - 5spd Rice Haters Club member#105

01-05-2003, 08:14 PM	#4
stang4to8 Registered Member Join Date: Aug 2002 Location: new hampshire Posts: 48	jerking i second that, replace those o2 sensors & reset the computer by diconnecting the neg. bat. cable for 20 or so min. reconnect after said time & take it for a drive for awhile so car can relearn fuel curves. i sure hope you already gave it the full tune up! anytime a car starts w/ these kinds of problems, go after the easy stuff first like all the tune up goodies.clean the idle air bypass solenoid also. __________________ 1988 Saleen reproduction Red H.B./Gray Saleen FloFit int. Racecraft suspension Saleen/SVO 5 lug disc brakes Saleen 5 lug mesh wheels

01-06-2003, 08:08 AM	#5
HiFlow5 0 Registered Member Join Date: Mar 2000 Location: Springfield, Ma, usa Posts: 706	Do you have any mods on the car, like a cam or anything? Your jerking problem sounds like what my car did before I got a stall converter matched to my cam. But if the oil pressure drops at the same time, sounds like you might have a more internal problem. __________________ NewEngland Auto www.baystategearheads.com -91 Mustang Coupe, ex 4cyl (sold) -99 F150, 3" lift, 35" Procomps, Magnaflow exhaust

01-06-2003, 02:29 PM	#6
XR1stang Registered Member Join Date: Apr 1999 Location: San Francisco, CA Posts: 205	heh, I have this same problem with my 94. I have heads, cam, full exhaust, etc. and this all started shortly after I did this. I just put in a new clutch over the weekend and the jerking went away for me. I have a 70mm BBK throttle body, but right now I'm running the stock one. The BBK had a problem with TPS voltage being WAY out of wack when I installed it. It was reading 1.35 with the original TPS, so I replaced the TPS and it came down to around 1.15 but was still high. I reinstalled the old throttle body and the TPS went down to .91 so I'm guessing something is screwy with the BBK piece somehow. Oh, my problem could also be coming from the fact that I have no EGR at the moment.... /shrug XR1stang __________________ I used to hate computers, until the server went down on me...

01-05-2003, 04:05 PM	#3
1989stanger Guest Posts: n/a	I had the same jerking prob and all that happened and that was because i did not put the downstreamtube back to the air pump for the cats but i have no cats so i left it off and someone told me that it should be put back on. Since having an off road pipe my o2 sensors were shot and check engine light would come on and engine wont performe at low speeds, so i bought some new sensors and havent had the problem since. So if you have an off road pipe then try that and see what happens.

01-06-2003, 06:05 PM	#8
69fastback IRAQ VET Join Date: Feb 2000 Location: high desert California Posts: 1,480	The car has shorty headers into an off road h-pipe so that sure could be my jerking problem. They only thing is the oil pressure drops too 1989 stanger did it make your oil pressure drop too? I know the 02 sensors are not hooked up so that could be the problem. Not sure of what all mods it has i bought the car at a dealership and the guy didn't know. Not sure what the idle air bypass silonoid is? __________________ 428 Cobra Jet SOHC 5.4 3V F-150 96 mystic cobra 91 GT

01-08-2003, 01:29 AM	#10
Shogun Registered Member Join Date: Feb 2002 Location: Nebraska Posts: 86	69fastback, clean your Idle Bypass Solenoid (IBS) throughly, the IBS is located on your Throttle Body facing the front of the car left side, it is postioned at a 45 degree angle in relation to your TB. It has two mounting bolts and one electrical connection. Once that is clean, remove and replace the Intake Air Temperature (IAT) sensor located on the right side of the intake (lower) behind the coolant temp sensor. This sensor may be gunked up a faultly IBS. This sensor helps to control Air Fuel ratio in open loop. Also, replace those O2 sensors, you are KILLING your performance and fuel economy by not having them present. They communicate directly with the EEC-IV during closed loop operation monitoring the amount of O2 in the exhaust which in conjuction with other sensors helps set air fuel ratio etc.. OK, getting wayyy off the subject. Try those first. Oh, one more thing, I think the reason your having problems, I believe your EEC-IV is running in Failure Mode Effects Managment (FMEM) this occurs when you lose a sensor or one goes out of range. The computer has preset values to cover that damaged/dead sensor and your engine will operate but not to its full potential. Ok, too long I know. But to Qutoe NBC "The more you know".. Hey anyone feel free to jump in if I stated something wrong. __________________ Proud RHC member #99 1990 Mustang GT Trick Flow heads,F303,Mac cold air,FMS 65mm tb,73mm ma,FMS 1.6,GT-40 intake,MSD igintion,NOS Big Shot@150,Mac equal shorties,Mac h-pipe,American Thunder flows,Centerforce dual friction,TTC 3550,alm drive shaft, 3.73's, HPM subframes, k-member brace, strut tower brace.. amongst others.

01-11-2003, 05:58 PM	#11
1989stanger Guest Posts: n/a	It did drop but not low enough to worry

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