Hello all. If possible I'd like a little help with my idle. My current problem is that I'm struggling to get my MAP values down, and therefore the car is idling very high, a minimum of 1100 RPM. It wants to sit somewhere around 50kPa, even with the IACV at 0% duty. I've looked over everything I can think of to rule out the simple problems, but wasn't able to find anything obvious.

Things I've tried:
Idle valve test mode, running at 0% duty cycle. Resulted in a minimum RPM of ~1100. ~50kPa.
Check vacuum lines for leaks (all lines are new silicone)
Replace throttle body gasket.
Replace throttle body.
Replace intake manifold gasket.
Check torque on manifold and throttle body.
The EGR system was deleted, check EGR block off plates for leaks, add RTV gasket to EGR block off plates. Check for fitment.

Attached is my MS3 map and of idle with some throttle blips. Is my calibration set correctly for the MAP sensor? I have a MS3 Pro PnP, which I believe uses the MPXH6400. I have the values set to 3.5 kPa at 0.0Vdc, 416.5 kPa at 5.0 Vdc (I believe these are default). MAP reading with the engine off is around 100 kPa, which is correct according to my local airport (Twin Cities MN).

Anyone able to provide some insight? I think I'm at the point where this is the thing that is stopping me from progressing my work on the car. Been working on it on and off for the past few weeks, without any perceptible progress at all. I'd really appreciate any help you can provide, or at least point me in the right direction.

Thank you.

 

On some versions a DC of 0 will result in a higher idle than a DC of ~25.

 

Idle bypass screw too far out?

 

Thanks for the suggestions. I've stepped through the range from 0-80% duty to find my bounds, and 0~28% behaved the same with respect to the MAP.

One of the reasons I swapped out the throttle body was because I ended up changing the idle screw setting too much, to where I couldn't find home again. I progressively closed the screw until the engine was choking and knocking, but it didn't do much at all to the MAP reading. Kind of why I suspected a vacuum leak, and tore everything apart. Figured swapping in another throttle body would give me a known good, and may solve the problem. It did put me back at square one, to where the engine is not knocking anymore, but didn't help the idle RPM in any noticeable way.

Some added info, the car is a 99 NB that I swapped a VVT into. Car is naturally aspirated. I purchased the car when the previous owner threw a rod and didn't want to fix it, and the new engine is an unknown to me as well. I'd assume the idle screw setting was fine for both engines prior to me messing with them.

I do see in the log that the pressure drops to 36 when i let off the throttle. I'm not sure if that is meaningful?

 

A car that runs poorly requires much more mani pressure to maintain idle. At 1100 you should actually be pulling more vac than you would at 800. My first guess would be cam timing if you can choke the engine with the idle screw.

 

Interesting. I have checked the spark timing multiple times, and it is as close as I can get it. This may be a dumb question, but is there a way to check the cam timing without removing the valve cover? Also, I'm assuming you're thinking about the intake cam? I can pull the valve cover tomorrow to take a picture if it would be of use.

I did have some timing issues early on, where my intake cam was timed in phase with my exhaust cam (dumb mistake not understanding the timing procedure with the VVT cam gear), so I've been overly sensitive to timing issues. The VVT aspect of this engine has thrown me for a loop. I've been running with the solenoid unplugged and VVT disabled in the tune to simplify things until I get everything working smoothly.

This may or may not be related, but I've noticed that my spark timing is not nearly as consistent as my NA miata, where the spark time does not fluctuate or deviate at all, but this engine will jump around a few degrees.

 

Also check the vac line running to the MS (all the way to the MAP sensor, not just the case port), I have seen that get pinched and cause the car to run like ****. Mistimed ex and/or int can eff up idle vac. Can't you see the timing marks with the lower cover removed?

To put things into perspective, my motor would hit rev limit at 50kpa, and I am driving a 1L SC and have back pressure from an ex turbine.

I rarely open logs anymore, AFRs in check?

 

AFRs are rich in that log, but yes I can get them to be in the 14 range pretty easily by changing the VE table. VEs around high 20s, low 30s in that rev range to get into the 14s. I've checked the run of the vacuum line to the ECU multiple times, but have not opened up the box to check the internals. I'll see about doing that this week.

I've attached a picture of my cam gear timing. I'll still open it up again tomorrow to have a look, since I'm not 100% sure this was before or after I resolved the intake cam phase issue.


cam timing

 

Hope it was before, if you are at TDC that intake cam is way off.

 

Most likely. You're looking at the small dot on the intake cam gear? I'll tear it apart to recheck tomorrow evening.

 

The timing mark isn't even in the pic. That dot should be located about where the belt intersects the pulley from the tensioner pulley after the crank gear.

 

Ah right. I checked the date and that picture is from about 6 weeks ago, and from the looks of it the car likely would not start. I'll take another picture tomorrow evening. Anything else you recommend I check while I'm in there? I really do appreciate your help so far.

 

Confirm fixed spark timing and that the locking pin in the phasor is engaged

edit: and if you can see the crank cog notch, confirm that when it is vertical (TDC) the pulley indicator lines up with the 0 degree timing mark on the lower cover.

Slipped pulley

 

You're thinking the VVT actuator might be moving around? I'll take the cover off and take some pictures.

 

I don't think pictures will show it, but yes, that is something to check. The cam should be locked to the sprocket.

See edits above

 

I do have a spare pulley from the other engine, while I'm in there I might think about swapping that out as well? Not like it's difficult, if you're thinking it may be a slipping pulley. I'd hesitate to change too many things at once though.

 

this is why you inspect prior to replacing parts.

 

Results. I'm not too sure what to look for regarding a slipped pulley. All pictures where taken as close to crank top dead center as I was able. Timing does appear to be a couple of teeth off on the intake cam, as suggested. Also not entirely sure what I am looking for with the VVT actuator. How you see it is how the cover bolts on.





I did reference this post when looking at the VVT actuator. Of course when I took off the cover all the little springs etc came out. https://www.miataturbo.net/engine-pe...or-pics-80407/

 

Bummer about the apex seals, for future reference when you remove the valve cover you can check locking pin engagement by rotating the timing belt clockwise and counterclockwise and confirming the cam is in synch with the sprocket. I hope it goes back together for you!

That intake cam is way off. That could certainly result in poor idle quality.

Edit: crank pulley looks good

 

Yeah sorry that picture was taken before I got all the seals and springs back together. Everything is accounted for thankfully. I went slow when I took it apart, so most of the bits stayed put in the oil film. I removed with a magnet and reassembled on the bench.

A fair amount of oil got onto the timing belt when I took the actuator cover off, so I'll pick up a new belt tomorrow, put it all back together, and give it another shot. Again, I really appreciate all your help. I think my error was in researching timing procedure with the OEM ECU, most write-ups instruct you to get the intake timing close enough, so that the ECU can compensate. Doesn't work too well when I disable that feature.

I think I've had this valve cover off so many times I bet I can do it blindfolded. Only one way to learn...