Rough idle and surging

So I've had this problem off and on for a while, but now it's gotten pretty bad. On warm startup sometimes the RPMs will dip too low and the car will just shut off. Other times it will just dip low and wander back and forth before settling at idle. Sometimes it will just go straight to idle with no problem. Then when driving, as I stop at a stoplight, the idle would wander a little bit before settling.

To try to fix this, and just for general maintenance, I replaced all the vacuum lines and the cam position sensor. The problem got better, but never completely went away.

This past weekend I replaced my radiator, and during the install I disconnected some parts of the intake, reinstalling them all completely after the radiator was in. It ran like normal for a few days until today.

Today, the startup was even worse than usual, the idle has been extremely rough, and I'm getting surging with a lot of throttle. Does anyone have any idea what might be causing this?

For a little additional info, I have an intake installed that relocates the MAF to after the intercooler ('04 MSM) to help with some MSM ECU quirks. This may or may not be causing issues, but the startup issue was also a problem before I added the intake.

Dirty MAF perhaps?

Have you pulled codes?

No codes have shown up. I'll pull out the MAF and give it a quick cleaning.

Does the MSM have the same intake manifold as other NB's? There's an EGR port inside that may need cleaning.

See this link - Steps 15-18

http://www.miata.net/garage/manifold/index.html

Thanks for the link. I'll give that a shot as well.

Question - Wasn't the above intake issue a 1999-2000 exclusive problem???

The 2001+ VVT cars don't seem have the same issue.

The MSM actually doesn't have the VVT. Searching the MSM forums it seems like the EGR valve itself is likely to be the source of my woes. I found a link to this thread from the protege forums: http://www.mazdas247.com/forum/showt...Rough-Idle-Fix

It sounds exactly like what I'm experiencing. The EGR valve is in a different place on our cars, but I'm gonna give that a good cleaning today and see what happens.

Isn't the MSM basically a 99-00 motor with lower compression?

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Originally Posted by OZMDD

Isn't the MSM basically a 99-00 motor with lower compression?

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This is correct

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Originally Posted by stinkydragon

It sounds exactly like what I'm experiencing. The EGR valve is in a different place on our cars, but I'm gonna give that a good cleaning today and see what happens.

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The 2 EGR ports inside the manifold pass thru to each other. I used a piece of weed-eater line like a plumbers snake to clear that passage. I also used a few hundred q-tips and a couple cans of throttle body cleaner. ;)

Well I cleaned the EGR valve itself today, and it didn't fix the problem. I'm going to clean out the MAF tonight, and I'll take apart the intake manifold to clean that later this week. If the EGR ports are what's clogged I guess it wouldn't be much help to just clean the valve.

1. Check to make sure the throttle body butterfly is closing completely at idle. I had the same symptoms after doing something where I had the throttle cable disconnected for a while and it needed to be stretched again.
2. Move the vacuum line from the bottom of the intake manifold to the 'boost sensor' to the port on top. Take the cap from the port on top and put it on the bottom. The bottom port gets clogged earlier than the top one.

My PSA for this evening: CHECK YOUR GROUNDS

I pulled apart my intake and gave the MAF a thorough cleaning, tightened everything back up, confident it would fix the problem, and I started the car to find that nothing had changed. Eventually I noticed that it finally threw a code (P0102 low signal from MAF) and I was pretty dismayed. I was about to start ordering a new one, when I decided to check the ground for the MAF. There's a place where the harness grounds to the top of the intake manifold near the throttle body. I gave it a good cleaning with some throttle body cleaner (lightly) and a brass wire brush. When I started the car up again, the problem was totally gone.

So almost a year of pulling my hair out (it didn't get really bad until Tuesday), a couple dozen new vacuum hoses and hose clamps, and it all came down to one bad ground. Just glad it was something easily fixed!

Good job, glad you figured it out.

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Originally Posted by sammm

Good job, glad you figured it out.

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+1

Alright, well I'm stumped again now. The problem has slowly resurfaced, which makes me think it might have actually been a dirty MAF to begin with. When I cleaned it off, I might not have given it enough time to dry before sticking it back in, and the residue from the MAF cleaner could have caused it to show a bad reading when I first started it up again. It wasn't until after it had been sitting around a while (and conveniently until after I tried fixing the ground) that it started working well again.

So any more advice? I'll probably try cleaning out the intake manifold. My feeling is that after the intercooler is a bad place for the MAF, so I'm going to try putting it back to the stock intake setup for a while. If that goes alright, I'll probably ditch this intake and go for the FM one since it leaves the MAF before the intercooler.