jfunkf150

I have a 97 and I recently straight piped it from cat back and put shifty headers on the truck runs fine except for when I downshift to a stop one I'm stopped the idle will fall low and then rise back up again. I'm thinking it from low back pressure but not sure any thoughts

DrillRig52

Mine was doing this for a while. Then one day it would not start. Replaced the fuel pump and it is smooth as glass now. I think its called surging, fuel pumps are known to do that before they go out.

saegernyles

Mine does the same thing when I come to stop signs or traffic lights. Rpm's will be normal and then they will go down around 500, all my lights will get a little dimmer, heat will bog down a little and then it will shoot back up to normal. Happens real quick too. It's bugging the crap out of me!

jfunkf150

I talked to my college professor about this today he told me it could be the back pressure in my exhaust since it is straight piped. I noticed it also does it at higher rpm downshifting when there is back firing

DrillRig52

Mine is straight piped as well. Doesnt do it at all after replacing the fuel pump. You can get it pressure tested and save yourself some grief later if that is the problem.

jfunkf150

I think I'll try that tomorrow at work

DrillRig52

Good luck man. Hopefully its something less expensive!

FunkSkunk

Its probably a vacuum leak, and based on the braking symptom its probably related to your brake booster going out. maybe a random hose with a crack in it too. Check those and let us know

jfunkf150

No it has nothing to do with breaking it's when downshifting if I shift into a lower gear and then press in the clutch my idle drops real low then comes back up. When I just press the clutch and brake nothing happens it stays normal

Jbrew

When does it pick back up again ? Need more info. What's warm idle at in Park or N?
Idle should always be very close to 730 rpms at warm idle and coasting to a stop in gear.
If you really want help, you need to test a few things and be as accurate as possible.