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1991LS400

Engine Rpm's Drop At 3K...

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Car: 91 LS 400

Problem: When stepping on the gas pedal (accelerating), the engine speed/RPM's drop whenever I hit 3k RPM's and then "kicks" itself back into gear before attempting to reach over 3k RPM's during acceleration. If I let go of the gas pedal and then try to accelerate again, as soon as RPM's hit 3k, it drops again and then "kicks" itself back into gear (or regular speed) while accelerating. Basically, the car "pulls back" on me for a second at 3k RPM's every time when accelerating and then lunges forward as if it's regaining it's normal speed/RPM's.

Before I keep on rambling, does anyone have any ideas on what could be causing this? I hope I made my symptoms clear. Thanks in advance.

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Does it do the same when in park/neutral and you rev to 3000RPM?

It could be a "flat spot" on the TPS.

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Does it do the same when in park/neutral and you rev to 3000RPM?

It could be a "flat spot" on the TPS.

Yes, it does the same when in park/neutral. How do you diagnose a "flat spot" on the TPS? Don't crucify me for this but my TPS was purchased new from AutoZone a few months ago. I wouldn't think such a small part like that would make much difference from OEM, right? Maybe I didn't adjust it correctly as I'm not sure how to go about doing it.

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Have you ever cleaned your throttle body? -> http://www.lexls.com/tutorials/EFI/throttlebody.html

Just wondering if maybe it is "hanging up" or sticking momemtarily at about the 3k mark.

Yes, TB was cleaned when it had to be removed to replace the starter. I'm thinking it has something to do with the TPS, like steve2006 said. Just not sure how to go about checking it.

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Yes, TB was cleaned when it had to be removed to replace the starter. I'm thinking it has something to do with the TPS, like steve2006 said. Just not sure how to go about checking it.

Have you gone through this? -> http://www.lexls.com/tutorials/EFI/tps.html

It is especially interesting to note what the author says within this tutorial..."My first test drive the sensor was set too low and it caused very jumpy highway performance."

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Yes, TB was cleaned when it had to be removed to replace the starter. I'm thinking it has something to do with the TPS, like steve2006 said. Just not sure how to go about checking it.

Have you gone through this? -> http://www.lexls.com/tutorials/EFI/tps.html

It is especially interesting to note what the author says within this tutorial..."My first test drive the sensor was set too low and it caused very jumpy highway performance."

I've read through that and attempted to follow it but I'm not sure whether I'm supposed to be doing the TPS adjustment when the car is on and in PARK or on and in DRIVE or NEUTRAL. Because in PARK, my car is idling at 1,300 RPM and in DRIVE or NEUTRAL it's idling at around 800 RPM.

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[

I've read through that and attempted to follow it but I'm not sure whether I'm supposed to be doing the TPS adjustment when the car is on and in PARK or on and in DRIVE or NEUTRAL. Because in PARK, my car is idling at 1,300 RPM and in DRIVE or NEUTRAL it's idling at around 800 RPM.

I would imagine the author is speaking of RPM's while under load. ie: in drive while idling with the brake on and fully warmed engine.

Your engine runs at drastically different RPM's when in park vs neutral(both no load) AND a fully warmed engine?

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The idle speed in park with the engine fully warmed should be around 650,I would follow the procedure given and set up the TPS correctly and then if the fault persists go from there.

You can check the TPS output voltage with a meter set to DC volts,the old needle ones are better for this as you can actually see the needle flicker at a dead spot as you move the TPS,the digital ones react slower making it harder to see a glitch.

You mention that the TPS is a replacement,why did you replace it? and was the car doing this before replacement?

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