RPM’s Dip, Almost Stalling in Reverse

[AWE46M3]

Hello Group,

I have a SMG to Manual swapped M3. I recently installed the NLA brown clutch switch, which has resolved almost all of my random stalling issues. Cruise control is fully functional and I have no “Switch Grip” faults.

Unfortunately, one lingering issue remains - when my car is warm and in reverse going down a slight decline (backing out of a slanted driveway, reversing downhill) my RPM’s dip to below 500 and the car almost stalls out. Hitting the brakes triggers the dip, which leads me to suspect this is a vacuum related issue. CCV, ITB, and checking the various vacuum lines I have are on my list of things to investigate.

RPM’s are high enough during a cold start for this not be an issue. I do not have this issue reversing the car on a flat elevation (likely because I am not applying the brakes hard enough to trigger it).

I’ve been doing some research on old E46 sites and haven’t found anything promising. Looking for suggestions on things to check and verify. Any feedback you all have would be greatly appreciated. Thanks in advance 🤝

[Nate047]

Does it also do this in 1st gear, stop and go traffic? Did you look at your fuel trims?

[AWE46M3]

Does it also do this in 1st gear, stop and go traffic? Did you look at your fuel trims?

Never had the issue in first gear. Not to say it isn’t possible, but I usually start in first and rarely come to a complete stop while I’m still in first. Stop and go traffic I’m usually in second and will throw it in neutral if I need to come to a complete stop and then start back out in first when things get moving again.

I have not checked fuel trims - I don’t have the equipment for that. Any recommendations? You think fuel pump is lagging pushing fuel up to the injectors when I’m in a decline?

[Slideways]

This typically happens with a vacuum leak.

[AWE46M3]

This typically happens with a vacuum leak.

Installing my airbox and planning to replace my PCV and hoses connecting to and from the airbox. Should replacing these parts cover all bases? Let me know if there are any other vacuum lines or related parts I should consider replacing while I’m at it.

I’m planning on installing a Radium catch can when I do the airbox but do not believe that should adversely affect the vacuum system.

[ugaexploder]

You did mention it so I'm curious...what else did you do to verify everything was working properly after installing the brown clutch switch? What was the one you replaced? Was it a black 700 switch?

Did you do a partial read on DME, check to see what was changed in .bin file, and verify checksums to see if SMG was coded out, etc, etc, etc? Or was it basically an install and pray?


When we start talking about hardware issues, I think some assumptions are being made that the conversion is complete and solid. I'm thinking you need to hash out the conversion and verify if possible.

You mention that it solved almost all of your issues. This statement alone makes me believe some things weren't verified. I would do this before you start spending time and money on a vacuum leak or fuel trim issue.

[AWE46M3]

You did mention it so I'm curious...what else did you do to verify everything was working properly after installing the brown clutch switch? What was the one you replaced? Was it a black 700 switch?

Did you do a partial read on DME, check to see what was changed in .bin file, and verify checksums to see if SMG was coded out, etc, etc, etc? Or was it basically an install and pray?


When we start talking about hardware issues, I think some assumptions are being made that the conversion is complete and solid. I'm thinking you need to hash out the conversion and verify if possible.

You mention that it solved almost all of your issues. This statement alone makes me believe some things weren't verified. I would do this before you start spending time and money on a vacuum leak or fuel trim issue.

almost all issues - the “almost” being this final issue where I stall in reverse down a decline. Hitting the brakes triggers the RPM dip. I had all the common stalling issues people with the black clutch switch have prior to installing the correct switch. No longer issues now.

Switch was installed by EAS in SoCal. Tom verified the coding/DME and Steve cleaned up some wiring issues I had from my previous switch to the DME (swapped by previous owner). If the switch was not working properly, I’d still be stalling intermittently and I would not have cruise control functionality (as the ground in the switch is essential for that to work). I did not have functional cruise control with my old switch.

I’m going to replaced the hoses that connect to the bottom of the airbox (ICV hose, PCV repair kit) and take it from there.

[ugaexploder]

You had someone else install the clutch switch and check the coding, but want to rule out verification when it only takes a few minutes? I’m sure EAS is top notch, but that doesn’t mean you can’t do yourself a favor to verify the work.

Just because they got your cruise control working does not mean everything was coded properly nor the clutch switch was bad. It has been proven the black 700 switch works fine. But hey, if you like it I love it. Sounds like you have your mind made up.

[AWE46M3]

You had someone else install the clutch switch and check the coding, but want to rule out verification when it only takes a few minutes? I’m sure EAS is top notch, but that doesn’t mean you can’t do yourself a favor to verify the work.

Just because they got your cruise control working does not mean everything was coded properly nor the clutch switch was bad. It has been proven the black 700 switch works fine. But hey, if you like it I love it. Sounds like you have your mind made up.

If the issue persists after the vacuum lines I mentioned are replaced, you’ll be the first person I reach out to for tests and checks I should run 🤝

[bhoom_S54]

Did you get this resolved? I recently purchased a car that was manually swapped many years ago and is having the same. Sometimes when putting in reverse, RPMs dip so much that it actually has stalled 2 times on me

[jdamore44]

I've had an issue since my smg to manual swap where my car wants to stall when backing up. It has all the proper coding and switches for the manual. I'm going to try a Smoke test soon and see how that goes. another issue I've had, even before the swap was when I blip my throttle at idle it will stumble for a split second before revving up. Drives me crazy. New fuel pump, spark plugs, rebuilt injectors, new coils. Head scratcher.

[bhoom_S54]

I've had an issue since my smg to manual swap where my car wants to stall when backing up. It has all the proper coding and switches for the manual. I'm going to try a Smoke test soon and see how that goes. another issue I've had, even before the swap was when I blip my throttle at idle it will stumble for a split second before revving up. Drives me crazy. New fuel pump, spark plugs, rebuilt injectors, new coils. Head scratcher.

Definitely interested to know how the smoke test goes. Mine has the exactly things happening. And mine was also swapped from SMG to manual.

[Notan_S54]

I have this issue when coming to a stop. Also a manual converted car. PDC also doesn’t work but that’s a whole different kind of issue.