Hey guys, I've been trying to track this issue down on my 2.8 Sport Coupe but it keeps showing up. When the car first starts up and gets to a stop, she'll idle just fine. Once the car hits operating temp (180*), there's a noticeable bog/stumble while stopped on the brakes.

I've rebuilt the parts ignition system (new coil, ICM, pickup coil, cap & rotor are fine). Injectors are brand new, fuel pump less than a year old. Sometimes while stopped, esp when using blinkers, my volt gauge reads low-but I've checked at both the alternator and the batt while running and it reads a healthy 13-14 volts on both while this happens. Something's backfeeding with my blinkers? I could hear it thru the right speaker too (only my left front one works ) Maybe something's backfeeding and causing the stumble?

This is what I've been leaning more towards-The other thing I was considering was a vacuum leak thru the power brake booster. All my lines are intact and factory, but my brakes can be iffy at times. Usually the brakes feel firm, when they're especially firm and you come to a stop the car definitely doesn't enjoy idling. Other times the pedal nearly floors. Oh, and it whooshes when you hit the pedal. More I look into this the more it sounds like my booster is shot, haha

Should I look into replacing just the power booster, or the master cylinder as well?

Any advice/things to check is appreciate guys, thanks

 

Just a shot in the dark here...have you tested the tps, maf, or iac?

 

I haven't, but the more I look into it the more I'm faulting the booster. Hard brakes, stumble at idle, I think I'll look into or replace it first. If that doesn't help I'll check those next, thanks

 

If the brake pedal goes really hard and you struggle to pull her up then the boosters dead, if the pedal goes to the floor that's not the booster that's a brake issue . Your sure the cars fine when cold ? , then it's a temp related issue like a coolant sensor not letting the car switch closed/ open loop. Or I had a vac leak on mine but only when warm ! Everything expanded including the leak lol .

 

Yea I was thinking about how it only happens when warm, maybe the leak doesn't happen when it's warm, but when the brakes & booster are "warm"...pedal's definitely hard tho, so I'm gonna look into the booster in the new few days.

 

Ran some tests on the car today- Holds vacuum at 16hg, stomping brakes doesn't affect the gauge, but stomping fast enough the car acts as if she'll stall. She was idling fine thru the stops in a drive thru, then started acting up at a red light. Guess I'm replacing the booster tomorrow...

 

Well if anything hopefully you get a more consistent brake pedal fingers crossed it sorts out the stalling too.

 

Ran more tests and hopefully fixed the issue- TPS tested fine with .56/.57 volts with key on, responded well when moved up to about 3.88 at WOT/as far as i could get the thing to open.

Cleaned IAC- was COVERED in carbon. Got it and the IAC screw hole place all cleaned out with gum cutter (being careful not to get anything in the IAC motor ). Threw back together and went for a test drive. Car took right off, she's a happy camper! Brakes felt great, idled fine at a light. I'm still hitting up the junkyard for my 4th gen and a Pinto, so the drive there and back will be the ultimate test. Hopefully that was it, to think I about dropped $150 for a new booster yesterday

 

Haha nice one. TPS wot voltage seems low does it not ?

 

A bit, I read it's supposed to read around 4.50 but the most you're likely to get it to read is around 4.0, haha

 

I was under the impression wot was anything over 4v .
yes.
https://www.thirdgen.org/tpimod2/
You may not be getting wot.