Let me start this story with a few disclaimers. First off, only in the loosest possible sense and in very dim light could I be confused with someone who knows what they're doing. Secondly, I'm not a mechanic at all, and can only do the most basic tasks with a screwdriver. Anything beyond removing the engine cover is a daunting task for someone with my lack of skill and chunky fingers. Take this the tale - as-yet-unfinished though it may be - with those in mind.

I have a 2004 Mazda MPV, with roughly 143,000 miles on it. It's a good van, though it lacks any sort of glamour or really anything beyond the most modest features one could get in this vehicle. I'm the second owner. Aside from a few scratches and a few unsightly dings, she is in quite good shape.

Three weeks ago, toward late April, all of a sudden my check engine light came on. I have a cheap Amazon OBDII scanner and an app on my phone, so I hooked it up and it gave me the following code:

P0106 - Absolute Manifold Pressure something something something

Well, I pondered that for a bit, but the van was otherwise driving fine, so I cleared the code to see if it would recur (knowing that it would, because that's how my life works, but figuring I'd see.)

Three days later, the check engine light came on again. I hooked up my scanner and was presented with not one but TWO codes:

P0106 - Absolute Manifold Pressure something something something
P0401 - Exhaust Gas Recirculation Flow Insufficient etc etc etc

Okay, so, like Donny, I was definitely out of my element. I called my preferred shop, who's done right by me on several occasions, but they were literally booked out a month. I need a vehicle before that. I called my less-favored choice, a much closer but more expensive shop. They could get me in. I dropped off the van with them.

Many hundreds of dollars later, I picked up my van with a brand new EGR valve. She drove fine, and I was zipping around town in her on errands. That evening, however, the check engine light came back on. Here's what my scanner said:

P0106 - Absolute Manifold Pressure something something something
P0401 - Exhaust Gas Recirculation Flow Insufficient etc etc etc

I dropped it off at the shop the next morning. They took a look at it, said, "our bad, a vacuum hose seemed off so we replaced it no-charge", the light was gone, and I went on my way for the entire weekend. That Sunday, a little under a week and a half ago, I had been driving around. I got back in my van, started it up, and the check engine light came on again! This time, it was accompanied by an exceptionally rough ride, surging and idling very poorly.

I called the shop, but said I'd get the van to them mid-week. In the meantime, I went out to my local Autozone and purchased a replacement MAP sensor. It's on top of the airbox. Even I can replace that! The check engine light went off! However, tragically, the van was still idling poorly.

I dropped it off at the shop again. Several hundred dollars later, they replaced the Bank 2 o2 sensor (I believe) and said it was running much better. I went and picked it up and it seemed to be fine! The check engine light was off, though they had disconnected the battery, so of course it was. I got home, ran inside, then ran back out to run an errand I'd put off. My check engine light came on immediately. As it was Friday afternoon, I called the shop immediately but said I'd bring it back again at another point. I hooked up my scanner and got:

P0106 - Absolute Manifold Pressure something something something

Furthermore, I discovered that, while the van would idle well, it ran extremely poorly, surging and hesitating when I actually drove it.

And now we're here. I've exhausted my Google fu but I did some troubleshooting.

1. I checked both MAP sensors with a multimeter and a vacuum gauge. They appear to deliver a lower voltage as vacuum was applied, so I ruled those out as the problem, though I didn't check the exact values.
2. I checked for vacuum coming out of the EGR while the engine was running. Yes, there's vacuum.
3. I checked the boost sensor solenoid by applying power to it; it opens up when I power it and allows that vacuum through.

So, as near as I can tell, I'm left with either a bad PCM or a bad wiring harness. Both seem expensive and both are beyond my skill level.

Now, there's an outside chance that it's bad coils. I've had a problem with them in the past and replaced them roughly 50,000 miles ago. However, the van was running fine when P0106 first showed up, so I'd like to solve that before addressing the surging that could be the coils. Also, last time that happened it was occasional, not "suddenly showing up every time I accelerate".

Does the hive mind out there have any thoughts?

 

Sometimes a bad sensor or valve can cause something downstream to pop up as the issue and give a check engine light. It seems like you might be having issues with your idle control valve maybe? Also, I know the brake booster hose can get dry rot as well as a hose that goes behind the intake manifold. Check the hoses behind the throttle and make sure they are in good condition with no dry rot or cracking etc.