Hello everyone,

I have a problem with my rx7 fc turbo 2.
The engine was rebuilt like a year ago, everything was set by the FSM and Haynes book.

Since then there is a small problem that bothers me, I start the car, everything is fine, running good, idle is ok, everything seems fine. Actually this only happens when the car is not completely cold and started to warm a bit.
So I start to roll with it, as I said not completely cold just a little warmer and as soon as I come to a stop and let my foot off the throttle pedal, the rpm drops pretty fast but sometimes it stops around 500rpm (if Im lucky) maybe a little lower and pushes it back to around 1000rpm, but sometimes it completely stalls out and I have to restart it.

So the problem only occurs when the engine is not cold, neither warm but in between the two.
If its cold there is no problem and also if its warmed up the problem is gone.

I checked the TPS, BAC, Fast Idle screw etc, but I set everything as it should be.

Here in the forum I read before that the Dashpot could be the problem, cause it can stuck but its working fine, at least it seemed like there is nothing wrong with it.
I also read that maybe the break booster causes the problem since there is not enough vacuum, but we also replaced it and the problem didnt go away.

I read many things that could cause this kind of stalls, but we tried everything changed many parts since it was rebuilt and nothing helps.

Im kinda out of ideas, about what I can check.
Any ideas here what should I check or what could cause this problem?
Anyone experienced similar before?

Thanks for your answers in advance!

 

Is the thermowax set properly? It's the small wax cylinder that bumps the throttle open on cold-starts. It's designed to keep the idle at about 1500-2000 when cold and then taper to the normal idle when hot.

There is a check and set procedure in the manual, but if it checks out fine then don't mess with it. It can be a pain to reach it with the throttle body installed, so a mirror or something would be helpful to avoid removing it.

 

Thermowax is set properly. I went down the whole configuration process so I set everything step by step the thermowax also.

 

When you checked the TPS, which method did you use? I like the two-light method, but it's the most involved (unless you have the light tool already).

Otherwise I had good luck with the voltage method. Never got the resistance method to work for me.

 

When checking the TPS I always checked the resistance, I think that was documented either in the FMS or Haynes but I dont remember in which one exactly.
Is there better methods for TPS?

 

The OEM manual uses a special tool, it's a set of two lights. I believe it's a common 12V and then two separate grounds, and it plugs into the 3 pin green diagnostic connector under the airbox. I can take a picture when I get home later if that would help.

The way this works is that the lines on that harness connector go back to the ECU. 12V is just 12V, and then the two grounds are switched off the outputs for the Air Control Valve. One solenoid in the valve is active at idle, the other is active when not at idle. Or something like that, it's been a long time since I dug into it.

Since they're connected to these outputs, one light will light at idle and then turn off when you press the throttle. The other will be off at idle and then light up when you press the throttle. You tune the TPS by turning key to ON (car off), and the TPS screw so that only one light is lit. If too far one way then both light, if too far the other way then neither light. You have to get it just in the middle.

The reason I prefer this method is that it gives you direct feedback about what the ECU is seeing. The resistance method assumes that the wiring in the harness has 0 ohms of drop, otherwise the ECU might see those extra ohms of resistance and factor them into whether it thinks the TPS is at idle or not. Basically, you're working from the ECUs input side.

The light method comes from the ECUs outputs, which means you know exactly what the ECU thinks is going on. That being said, there is nothing wrong with the resistance method if it works for people. There is also the voltage method, which I had good luck with myself before I had the test light. It's worth trying the voltage method first before fiddling with making your own test lights. Basically you turn key to ON like I mention above (car not running) and then shoot for 1V of output across two of the pins (I think it's green positive and black ground) on the TPS. If the value is near 5V and not changing with turning the screw, then you have the wrong pin. I believe orange is the 5V pin, but I may have that backwards. Plenty of people use this method successfully.

 

Ah I see. Well all the time I had to set the TPS I only checked the resistance and it holds idle both when cold and hot so it might be close to the perfect setting.
If I set it also with the voltage method, the problem would go away? I mean if the resistance method is not really a good method, but we have idle, maybe we set it nearly perfect but that little to be perfect can cause this kind of stalling when warming up and coming to a stop?

Also, for the voltage setting the engine should be on operating temperature right?

 

For all methods it must be at operating temperature. Otherwise the TPS isn't fully closed due to the thermowax bumping the idle up.

I've had a TPS issue before (the harness broke actually) and my symptoms were that it would start and idle fine, and idle fine when hot too (a bit lumpy but not that bad) but then when coming out of gear and dropping down to idle it would die. I'm assuming the system in the ecu that kicks it into "idle mode" wasn't working properly due to the lack of TPS signal.

Now that's an extreme case since it was entirely unplugged, but a maladjustment could cause a similar issue.

 

I will definitely try the voltage method then cause I really want to get rid of this problem.
I really hope that this solves it cause I tried many things before but nothing solved it.

 

Oh, and one other thing. You verified the dashpot is working, but did you set it? I think the factory manual suggest having an assistant hold the engine at ~2300rpm using the pedal while you adjust the dashpot plunger to just barely touch the arm. Then lock down the lock nut.

 

Yeah I set that also. Thats why I was a little lost in this topic at first because I set everything as it was said in the manual and the problem still occured.
Actually since you help me with it, it must be the TPS (or at least I cant really think of anything else now) because thats the only part that I set only "halfway" cause I only set the resistance and never checked it like the other ways you told me.