2nd gen RX-7 non-turbo, idle issues when fully warm

[bast525]

Hey all, this is actually for a friend of mine. He's got a second gen non turbo RX-7, only mods are a K & N drop in filter, and full exhaust (headers all the way back).

His car runs well most of the time... when he first starts it, it fires right up, and runs smooth and makes good power. However, once it gets fully warmed up, it will suddenly want to die or idle very low and rough, it also smells like it's running really rich. He can keep his foot on the throttle to bring the RPM up and it will run okay, but if he lets his foot off the gas it drops very low and wants to die.

I don't know much about RX's, but I'm thinking this has to be something electrical, maybe a temp sensor or something that once it enters closed loop mode it starts to run really rich or something. Or any other sensor that the ECU only reads off of once the engine reaches a certain temp?

I just want to help him out... it's a nice car, he just bought it for like $2000, very clean inside and out.

I've already checked some things like vacuum lines and such and I don't see anything out of place or obviously old/cracked/damaged.

Any suggestions of where to start?

 

[evilmonkeyMSP]

Sounds like bad rotor compression....Time to have a compression test done and possible rebuild...

 

[bast525]

Sounds like bad rotor compression....Time to have a compression test done and possible rebuild...

??? seriously??

it runs PERFECTLY when started, and he can drive around for 10 minutes before the car acts funny. Also, on cooler days/nights, it will run fine, only when it's warmer out or like after he's driven on the freeway, then it will start doing it.

He took me for a ride, lasted about 10 mins, and for the whole time it ran perfectly, very smooth, good power, no misfiring or anything.

The next day, I pulled into the parking lot and he was sitting there waiting for me, he had just gotten to work, and the car did not want to idle.

 

[evilmonkeyMSP]

thats one of the signs...once its warmed up and cant hold idle or doesnt want to rev its usually do to bad compression

 

[bast525]

Yikes... I hope that's not it he just bought it.

Only has 60k miles on it.

are there ANY other possible causes? I was thinking faulty temp sensor or something like that.

 

[evilmonkeyMSP]

It might be leaky injectors also.... I would start w/ a compression test tho and go from there.

 

[melicha8]

Your problem is a leak(s) on the vacuum lines. A rotary, if the seals were bad, would run worst when it was cold. If I were to suggest a spot to look it would be in the rats nest. There are many short vac lines that could have cracks that cannot be seen I suggest replacing each line with silicon tubing starting first with the lines controlling the switching solenoids(colored or.,bl, br, ye) since it's effecting drivability

 

[bast525]

That was also one of my first guesses... I know that Rotaries have tons of vacuum lines running all over the place, and a leak in any one of these can cause all kinds of drivability problems.

I still suspect something electrical, just due to the very erratic nature of the problem. Today we met in the parking lot again, and this time the car was running perfectly after his half hour drive to work.

I did tell him that at some point he will want to go through and replace all of his vacuum hoses

 

[melicha8]

What rpm was he idling at and was he running accessories at the time? High idle can mask a vacuum leak like when you first start the car and accessories can aggravate a vacuum leak and cause the car to run poorly and stall

 

[aMaff]

I still suspect something electrical, just due to the very erratic nature of the problem.

Vac problems can be pretty erratic too. I had very similar symptoms on my miata, turns out there was a crack in the intake tubing past the air meter. But the problem would come and go sporadically.

What was fun once we found it was messing with the idle speed by opening and closing the gap LOL

 

[88rx-7turboII]

Mine did the same thing and after the compression test came back clean and no vac leaks were found we realized it was a bad IC ( idle control ) valve.

 

[Rotary_Powered]

Adjust the Throttle Position Sensor.