Having a weird issue with my sedan.


Its a fresh LDK swap. When I put my car in neutral and I am coasting at any speed above 20ish mph my RPMs will bounce between 500-1500. It idles fine at a stand still. Only when I'm moving. I recently noticed that my brake booster hose is dry rotted I ordered a new one waiting for it to arrive. No CELs. Car has a K&N intake and catback.









P.S. I know I spelled neutral wrong in the subject

 

If your brake booster hose is dry rotted and you have a vacuum leak it can cause your RPM to bounce but I would think that it would also do it when you are idling at a stand still. Is the idle RPM high when you are at a stand still?

 

nope it idles normal at a stand still and basically anything under 15-20mph

 

since your cars in motion, air is moving by where ever the leak is and causing your rpm issue. It might even just be air hitting your MAF. curious. just a guess though. id guess there is a disconnected vac line somewhere.

 

I originally though something like this. But the engine came with all the lines hooked up (I did check them over). The car does have a k&N but I never had this issue with the k&n on my other car if it is the MAF.

what do these cars hold stock? Mine holds 15psi and sometimes when I really get on it in 4th I will see maybe 16-17psi?

 

that sounds normal. 15 psi roughly, spikes to 16-17 psi.

I suggest not cruising in neutral lol.

 

I agree these cars do not line coasting in neutral with or with clutch pushed in.

I have found that if you do that and then try to drop into gear it will flood and backfire. It's a fun sound, but it's not necessarily good.

 

im fairly certain now that he mentioned he has an SRI, its just air hitting the MAF.

 

I don't understand though. my other lnf will coast all day in neutral and be fine.

I'm waiting for the brake booster hose and I hope that is the issue. but like you stated before it is definitely a vacuum leak.


the dry rotted part is right on the bend before it attaches to the intake mani. now that you said it has to do with air flow, I think it may be the issue.

 

I replaced the brake booster hose and it is still giving me the same problem

 

What are your afr's doing during this period? Have you logged it to see what's going on?

 

I rotated the filter and put the heat shield back in and drove it very briefly and everything seemed fine