Small driveability problem with 86 TPI car
Thread Starter
Instructor
Joined: Aug 2003
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From: Davenport Ia
Small driveability problem with 86 TPI car
Hey guys, thought I'd try to describe my problem as best I can although I think its not gonna be an easy thing to diagnose via the internet, but here goes:
Cars runs good most of the time, no SES light, have done most new tune-up parts and like I said, car runs very well overall. The small problem occurs mostly at cruising speeds. When I let off the pedal or drop down to almost no throttle, as in slowing to a lower speed, or letting off to cruise to a stop. The engine RPM drops to 1000 for a second, which actually pulls the car down like the motor is dead for just a sec, then it returns to around 1300 and corresponds with mph again. Its kinda hard to explain, but basicall the the rpm drops and returns to where it should be pretty quickly, but something makes it drop low for a second, which like I said results in the car really slowing for a second just like it died and then it comes right back. I have looked into some stuff, such as testing the TPS to makes sure it has no dead spot and it all seems fine. Anyone have any ideas or similiar problems???
thanks
Randy
Cars runs good most of the time, no SES light, have done most new tune-up parts and like I said, car runs very well overall. The small problem occurs mostly at cruising speeds. When I let off the pedal or drop down to almost no throttle, as in slowing to a lower speed, or letting off to cruise to a stop. The engine RPM drops to 1000 for a second, which actually pulls the car down like the motor is dead for just a sec, then it returns to around 1300 and corresponds with mph again. Its kinda hard to explain, but basicall the the rpm drops and returns to where it should be pretty quickly, but something makes it drop low for a second, which like I said results in the car really slowing for a second just like it died and then it comes right back. I have looked into some stuff, such as testing the TPS to makes sure it has no dead spot and it all seems fine. Anyone have any ideas or similiar problems???
thanks
Randy
Le Mans Master
Joined: Aug 2000
Posts: 5,192
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From: Airport Cruise-in 1 Veteran Airport Cruise-in 2 Veteran
Cruise-In II Veteran
Re: Small driveability problem with 86 TPI car (1986CE)
That sounds like a clogged or slow IAC valve. Pull that off your TB and see if it needs a cleaning. When you let off the throttle, the IAC valve opens up the IAC passage so idle air can get around the throttle plates. When you're on the gas, the IAC blocks off that passage b/c you have air entering through the open throttle plates.
If it's clean and you want to test it, measure the resistance between the "A" and "B" terminal and between the "C" and "D" terminals. Both should read between 40-80 ohms.
[Modified by War Machine, 2:38 PM 9/11/2003]
If it's clean and you want to test it, measure the resistance between the "A" and "B" terminal and between the "C" and "D" terminals. Both should read between 40-80 ohms.
[Modified by War Machine, 2:38 PM 9/11/2003]
Thread Starter
Instructor
Joined: Aug 2003
Posts: 113
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From: Davenport Ia
Re: Small driveability problem with 86 TPI car (vetracer)
car is an auto and engine rpm before i let off can be anywhere really. Basically just when I let off the throttle. I will check into the IAC, as that seems like a very probable solution.
Melting Slicks
Joined: Jun 2002
Posts: 2,168
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From: Phoenix AZ
Re: Small driveability problem with 86 TPI car (1986CE)
I notice a similar driveability problem in my '86 manual that occurs if I get the engine wet after cleaning it and the "Service Engine Soon" light comes on. My guess is that the engine has gone into open loop when this occurs. You might want to hook up a scanner and make sure your car is operating in closed loop.
Instructor
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From: South Cave, Brough East Yorkshire
Re: Small driveability problem with 86 TPI car (1986CE)
Hi, I have the same thing with my 86 Auto.
I assumed it was something up with the trans as opposed to the engine - but maybe i should look at my Iac valve as well.
Mine`s done it since i had the car - so for about 7500 miles - so i don`t think yours is gonna self destruct or anything - it wuld b interesting to c how many other ppl have the same thing - maybe its just normal ?
I kinda like it cos it sounds like a manual between changing down. I have to say that it doesn`t seem to slow the car down much in my case - just makes it feel like its free-wheeling a second. Does it in the same circumstances as urs though - low cruising speeds - will do it at 55 mph in overdrive if i let off the gas when exiting highway - but won`t do it if i let off the gas at say 75 mph. It does the same thing in normal drive but at a lower speed - say 40 mph.
Also, it is much more pronounced if i`m going down hill.
Hope its nothing major - could it also have anything to do with the TV cable ?
:seeya
I assumed it was something up with the trans as opposed to the engine - but maybe i should look at my Iac valve as well.
Mine`s done it since i had the car - so for about 7500 miles - so i don`t think yours is gonna self destruct or anything - it wuld b interesting to c how many other ppl have the same thing - maybe its just normal ?
I kinda like it cos it sounds like a manual between changing down. I have to say that it doesn`t seem to slow the car down much in my case - just makes it feel like its free-wheeling a second. Does it in the same circumstances as urs though - low cruising speeds - will do it at 55 mph in overdrive if i let off the gas when exiting highway - but won`t do it if i let off the gas at say 75 mph. It does the same thing in normal drive but at a lower speed - say 40 mph.
Also, it is much more pronounced if i`m going down hill.
Hope its nothing major - could it also have anything to do with the TV cable ?
:seeya
