Okay im having a issue that is quite weird. My idle is perfect at the moment but whenever I press on the brake my idle drops. Also when I do press on the brake hard I can hear a few clicks coming from the engine bay. Is the Brake booster dead? The brakes work though. We cant seem to figure it out.

 

What does your idle voltage look like?
Have you ran extra grounding cables?

Alternator could be weak or your charging system isn't up to par. Also, there is a solenoid on the throttle body to raise idle during electrical loads, such as headlights and A/C. I believe it's the ISC, but it's been awhile since I had anything attached.

 

We messed with all the idle adjustments and everything is in spec and car is suppose to idle at around 850 I think is where we set it. I have a Power FC in the mail so that should help me figuring it out. There also is no extra grounds, just the stock grounds.

 

I have the same issue when the motor isnt fully warmed up. Ill drive normally and as soon as I get to a stop sign the RPM dips and sometimes even stalls. I think the drop in RPM is bringing the map in to cell thats not tuned right (since the car usually doesn't reach those cells)

BTW i have extra grounds, PFC and single turbo. I think its either a tune issue or something to due with the TB adjustments.

 

Im still on stock ECU, Power FC should be here soon. TB adjustments were just done correctly and we noticed this after the adjustments.

 

Also remember that the clutch switch (one closer to the firewall) and the tranny neutral switch will inhibit the ECU's idle circuit from initiating if they are bad. This will cause idle to dip and stumble. Its easy to test their operation with a PFC, as it shows voltage or engagement of pretty much every sensor with the Commander.

 

How much does the idle drop? Could just be normal.

 

I'd say around 100 rpm. Enough to go down a tick mark if that makes sense lol.

Yeah power fc is here on Monday. I'll do a sensor check.

 

Try some extra timing and tune those cells a bit richer than your normal idle cells, helped my car alot under those conditions.

 

To figure out if it's a voltage or mechanical (vacuum brake booster) issue, unplug the vacuum hose going to the brake booster and cap it at the intake manifold Start car, run at idle, press brakes and see if there's a difference.

If there is, it's the load from the alternator. If it goes away, you may need to replace the vacuum lines going to the brake booster - there's a built-in check valve there that could be faulty.

BTW, when I changed to LED tail lights, I notice my dash lights don't dim now, way better than the stock incandescent bulbs.

Dale

 

I'll do that test. I will add this though, when I first built the car I didn't know there's a check valve needed for that line. My car was missing it all completely so I just plumbed a regular vacuum line. Problem was occurring.

Ordered the two lines and hard line from fritz and no change. This never happened while engine was breaking in but then again during break in idle never went below 1100.

 

I know that when pressing the brakes my car idle drops approximately by 70 RPM or so. I always thought it is because of the extra electrical load of the tail lights.

You can remove the tail light fuse and see if that stops the rpm from dropping.

 

Okay it does it less now, I unplugged tail fuse and whenever I press brake my lights dim slightly still.

Still does it with brake booster hose off and plugged at the uim.

Accepting the fact of just living with it. Rpm doesn't drop that much, car isn't stalling or anything.

Heres a video. You cant tell when I step on the brake very much but when I release thats when the rev up happens.

 

Noticed also that whenever I step on the brake I hear clicking, could be normal.