Long time engine rebuild - can't get it to idle - please help
 

Hello,

First, let me apologize that my first post here is one asking for help. Even though I'm only a few weeks new I've been reading the site for years and been on Miata.net since 2006.

I've posted this question a while ago on miata.net and didn't get a great response which is why I've turned to you guys. (this site always seemed much more technical and far fewer newbie questions. Is that enough kissing @$$?)

So as the title says, I rebuilt the engine over the last few years. Last year I got it running, and it moves under its own power but I cannot get an idle. As soon as I'm not on the gas RPM drops and it stalls out.

About the Car:
- 96M edition
- 99 head swap (swapped before the rebuild, yes it ran fine for about a year before I pulled the engine)
- M-tech rods
- stock pistons
- billet oil pump
- lots of other misc. suspension bits but probably not relevant to the idle issue.

Symptoms:
- Stalls out, sounds like it tries to hold the idle but just just sputters out.
- plugs get fouled quickly and are wet when I take them out.

What I've done:
- drained gas, purged lines, cleaned injectors, (one was cracked & replaced)
- confirmed timing is correct
- replaced nearly every vacuum hose I could. The only one not replaced is for the VICS on the 99 head.
- new plugs and wires (confirmed I get a spark on all 4 if I lay them on the valve cover
- Removed and cleaned the throttle body and the IACV. (confirmed the IACV does actuate when powered, not sure if I'm getting full activation or what to expect.)

All I can think of is a vacuum leak, but I have no idea where the leak could possibly be as I've inspected/ replaced everything I can think of.

Any help or things to try would be a huge help.

I haven't driven my Miata in 6 years, I'm sooo close to having her back.
+ I need to prove to my wife that it is actually a form of transportation and worth keeping. She has never even been in it, I pulled the engine just a month or two after we started dating.

Thank You

Oh and compression checked. 148 -150psi across all cylinders.
Also, NO check engine light and no codes are stored. that would be too easy.

Stock ECU so no way of logging what it thinks the temp is?

1. Seal the intake manifold and pressurize it to look for leaks with soapy water. I used a can of WD-40 clamped to the throttle body and an air compressor. 10-15 psi will be plenty. If you haven't replaced your injector insulators, they will be harder than hard plastic.

2. does it run at all with your foot in it?

Stock ECU.

1. I'll try something to that effect tonight. either incense or a cigar to try and see if/where its pulling air in that its not supposed to.

2. Yes, after I changed the plugs and wires, it runs fine (sounded like it was only firing on 2-3 cyliders). It does rev up very quickly. I think thats a result of the new lightweight clutch and flywheel.

Any chance fuel pressure and return lines are backwards?

No chance, I've triple checked.
I even switched them a couple weeks ago, won't even start if they're switched.

Sounds to me like you're flooding it out. Stuck injector? When you take your foot off, the butterfly closes and all that fuel chokes it. Look at the throttle body and cable adjustments.

plug the MAF back in.

I don't think its a stuck injector. I just pulled them and pressurized them with a syringe & hose over the top. No leaks and I actuated them with 12V to make sure they were all firing.

I've looked at the throttle body, removed it multiple times at this point. I've adjusted it so that the butterfly valve can just close all the way but still leaved tension on the cable.

Mixed feelings, I really really hope its this stupid simple.
But then again... WTF if it is.



I apparently left the key in Sunday, so when I got home last night... dead battery. Will be all charged and ready to go tonight. :x:

Oh man. Stupid but that would do it...

well...

No luck with the MAF, it was plugged in. I disconnected/reconnected and same issue.

I unplugged it completely and I got a CEL with codes P0100 and P0110. The car would start and immediately die. Even on the gas nothing would keep it running.

What else could be causing it to flood? The O2 sensor is new and confirmed plugged it.

Thanks,

Also,

I checked the timing, not sure how accurate but I was able to hold it at low rpm by keeping my finger on the throttle body. I could see it was about 10 degrees a the lowest rpm I could keep it running at. (ten & gnd jumped)

I got a fuel pressure gauge and checked the line closest to the the firewall that goes to the fuel rail. 40psi.
The return line coming from the FPR and going tothe line closest to the front of the car showed 0psi.
The car wasn't rnning I just jumped the fuel pump.

Sound normal?

Sounds like you just need to adjust the throttle stop

Adjusted the TPS last night and no progress.
It was very touchy, I was measuring ~50ohm most of the time and it qhickly goes to full open.
At least I know that at full closed there is continuity, which is where my problem lies.

Anything other ideas? I don't really want to just start replacing parts, I'm running out of patients with this thing.

Anything?

check the ground next to the TB. and the one behind the head.

Thanks for the input.

Both have already been wire brushed and secured.

What about the little screw on top of the throttle body that adjusts idle? I have had similar problems to you in the past and solved them by letting in a little more air at idle. Sometimes the idle control valve isn't capable of letting in enough to control idle.

You're getting signs of flooding/richness on the plugs because you're probably not getting enough air at idle and the startup fuel addition is not helping either.

Yeah, I've adjusted the crap out of that little screw. I started with it full in, then back it out 1 full rotation at a time starting the car each time and looking for a difference. maybe 12-15 times before the screw was flush with the TB housing.



So, last night I spent a little more time with a multimeter and found that the ground point on the front of the engine had higher resistance.
I was using a bolt on the head for that front grounding point and even though I had wire brushed/ sanded everything before hand it still wasn't a great connection.

I found the original ground point which had been pulled off the engine during the rebuild and I hadn't put it back on.
So after I got everything buttoned back up and went to start....

Same damn issue!

However, a few more issues arose as a result. The car run much more rough at low RPM now, AND I got a check engine light! T0120 TPS sensor.

I tried 3-4 more times to reset the TPS, erase the code, and try again.
But every time the code came back. I've got one on order now so we'll see how that works.

Also noticed that the enigne temp gauge isn't moving at all, even after i had run it for 5-6 minutes testing. Previously I thought it was because I never ran it long enough to get warm. So I'll be looking for that tonight/ tomorrow.