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89 LX dies when i let off the gas

4732 Views 6 Replies 2 Participants Last post by  Linson
the car: 1989 LX 5.0 AOD

the problem: it dies if you take your foot off the gas. it wont idle or nuthin.

when you start it, it fires right up, but once you take your foot off the gas, it dies imediately. doesnt stumble - just cuts out.

the problem has gotten worse because it used to idle but the idle was way low - like around 5-600 RPM. it used to run reliably, but you'd have to give it gas for about 3 minutes after a cold start up and it would occasionally die at a stop light. now it dies as soon as you take your foot off the gas no matter how long you give it gas.

it runs great and runs strong, but as soon as you take your foot off the gas - say to make a turn or at a stop light, it dies.

furthermore, i filled the tank 50 miles ago, and it is already down three eighths (five eighths left in the tank).

the car sat for a year because the trans was down, but it was doing this before, just not to this extent.

i purchased the car in May of '09.

tuned up? yes. new cap and rotor, and wires. new fuel filter. cleaned the throttle body.

replaced Throttle Position Sensor in June of '09. it shoulnt be the TPS, even though the car acts like it has a bad TPS. that helped back in June of 09, but the problem is back, and has gotten worse. and this ultra low gas mileage leads me to believe it is something else or at least something else additionally.

replaced the Idle Air Control module or whatever yesterday. that did nothing.

put the stock MAF sensor back on (it has a GMS unit). that did nothing.

any help would be appreciated.

btw, i havnt posted here for a while, here is a pic and my mods in case anyone is interested.

1989 Mustang LX Hatchback 5.0
BBK CAI, Pulleys, BBK equal length Shorties, ORHP, Flowmaster Force II cat back, GMS MAF, BBK subframe connectors, 3.55 gears, SSBC brakes-front, SSBC drum to disc conversion - rear, B&M 2000 stall, B&M console Hammer...more to follow.
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Have you pulled codes? That should shed some light on the problem.

Have you tried to adjust the throttle plate adjustment screw? Using that, you should be able to get it to idle. It may not be a perfect idle, but it will at least let you drive it.

Your IAC could have been fine, but merely had a damaged wire leading to it or from it. That would explain why the new one had no effect. That is, assuming the IAC is the problem. When you pull codes, you'll know more.
its not throwing any codes.

throttle plate adjustment screw? what is that? is that the little flate lever that the TPS envelopes?

i generally understand the concept of what youre talking about.

that still wont explain the gas mileage though.
yeah! adjusting that screw appears to have solved the problem of the engine cutting off. thank you for that tip.

now on to the 100 miles on a tank of gas issue.

a bad O2 sensor would throw a code, wouldnt it?
i remember replacing the O2 sensors when i bought the car, but as it turns out, a couple of the wires on the right bank (passenger side) were chewed up. replaced it and the gas mileage is back where it should be. :kooky:

thanks again.
1 - 5 of 7 Posts
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