fluxuating r.p.m needle

[supraman508]

Is it normal when you push on the brake pedal the r.p.m needle decreeses?

 

[Poodles]

bad ground...

The engine is slowing down because the load from lighting the brake lights is taking the energy away from actually running the motor.

 

[supraman508]

bad ground...

The engine is slowing down because the load from lighting the brake lights is taking the energy away from actually running the motor.

could that take away power from the engine?

 

[jetjock]

Assuming you have a normal hot idle of around 650 rpm to begin with the ISC system should bring it back up. If not open the idle bypass on the TB until you get a 200-300 rpm rise then wait until the ECU relearns the idle value and brings it back down. That could take a day or two but should completely resolve the problem. I'd explain why this works but I'm just not motivated right now...

 

[supraman508]

Assuming you have a normal hot idle of around 650 rpm to begin with the ISC system should bring it back up. If not open the idle bypass on the TB until you get a 200-300 rpm rise then wait until the ECU relearns the idle value and brings it back down. That could take a day or two but should completely resolve the problem. I'd explain why this works but I'm just not motivated right now...

Please do shoot me for asking this but where is the idle bypass.:icon_redf

 

[dumbo]

bad ground...

The engine is slowing down because the load from lighting the brake lights is taking the energy away from actually running the motor.

pretty sure that is total bs

when you step on the brake the atmosphere side of the brake booster diaphram opens, causing a major differnce in presure. engine vacum ---- atompshpere prssure. cant remeber exactly how it goes, but trustme its normal--within reason-- it dont stall you engine, slight drop is normal, my 86.5 does the same at idle, along with most cars i've owned. your engines "vacum" runs most brake "boosters" when you hit the brakes it has to "vacum" more area. acts as a load, damn been awhile since school, wish i could explain better.

 

[AJ'S 88NA]

Please do shoot me for asking this but where is the idle bypass.:icon_redf

I think it's on the front of the TB, has normally a black cap on it, inside there is a screw. If I'm wrong JJ will get around to correcting me.

 

[Poodles]

pretty sure that is total bs

when you step on the brake the atmosphere side of the brake booster diaphram opens, causing a major differnce in presure. engine vacum ---- atompshpere prssure. cant remeber exactly how it goes, but trustme its normal--within reason-- it dont stall you engine, slight drop is normal, my 86.5 does the same at idle, along with most cars i've owned. your engines "vacum" runs most brake "boosters" when you hit the brakes it has to "vacum" more area. acts as a load, damn been awhile since school, wish i could explain better.

First off... Look at my post count and when I joined.

I've BEEN through this, I had the EXACT SAME PROBLEM. It was the main battery grounds.

The brake booster has a check valve, so it is isolated from effecting the engine in the way you speak.

 

[ValgeKotkas]

Assuming you have a normal hot idle of around 650 rpm to begin with the ISC system should bring it back up. If not open the idle bypass on the TB until you get a 200-300 rpm rise then wait until the ECU relearns the idle value and brings it back down. That could take a day or two but should completely resolve the problem. I'd explain why this works but I'm just not motivated right now...

Explain it when you are motivated, please

 

[suprarx7nut]

pretty sure that is total bs

when you step on the brake the atmosphere side of the brake booster diaphram opens, causing a major differnce in presure. engine vacum ---- atompshpere prssure. cant remeber exactly how it goes, but trustme its normal--within reason-- it dont stall you engine, slight drop is normal, my 86.5 does the same at idle, along with most cars i've owned. your engines "vacum" runs most brake "boosters" when you hit the brakes it has to "vacum" more area. acts as a load, damn been awhile since school, wish i could explain better.

Do your rpm's drop slightly when you turn on your headlights? If you have stock wiring, the answer could be yes. Electrical components, whether it be brake lights or headlights can affect the "load" on the engine more than you might think. Especially when the wiring is 20 yrs old and at many instances thin and brittle and the grounds aren't making the nice contact that they once did.

 

[dumbo]

Sorry man didn't mean to sounds like a dick

i guess i never really thought about 20+year old wiring and what not.
but when you open the atomsphere side of the booster doesn't the other side suck in, wouldn't that take engine power?? its been awhile maybe you could re-enlighten me

First off... Look at my post count and when I joined.

I've BEEN through this, I had the EXACT SAME PROBLEM. It was the main battery grounds.

The brake booster has a check valve, so it is isolated from effecting the engine in the way you speak.

 

[jetjock]

Actually you're both wrong but here's an idea: Pull the booster line off, plug the port, and then see what the engine does when the brakes are applied...

 

[ILikeCarsYesIDo]

Do your rpm's drop slightly when you turn on your headlights? If you have stock wiring, the answer could be yes. Electrical components, whether it be brake lights or headlights can affect the "load" on the engine more than you might think. Especially when the wiring is 20 yrs old and at many instances thin and brittle and the grounds aren't making the nice contact that they once did.

My RPMs increase when I turn on my headlights.

 

[dumbo]

i got to thinking, and bad grounds, wiring in general, would cause a decrease in current flow-amps. wich means there would be less load on alternator-in turn less load on engine. so please do explain.

jetjock great idea.-but if were both wrong, what do you think it could be.