86.5 stock na hunting idle & stalling

[afofsupra]

Hi again

Ok, the car is up and running quite well. I suspect it may have an exhaust leak in the downpipe. All stock.

Problem: Hunting idle with the scale continually decreasing until almost stalling. When 1st started, it idles fairly steady at ~ 1000, after a minute or two it starts decreasing and hunting, (by hunting I mean bouncing in a range of rpms), it usually bounces in a 200 - 300 rpm range anywhere from 500 - 800 rpm on the low side to 650 - 900 on the high side. Mostly it settles on the low end.

Blipping the throttle over 1500 drops all the way back to 500 or less and often results in stalling.

(the following is per TSRM hardcopy)
ISC clicks & checks out properly
No codes reported (steady flashing CEL when jumpered)
inital timing set at 10* BTDC

I'm told the car has always had a slight hunting (bouncy) idle since new but has never stalled.

Could this be a vacuum leak or that the exhaust leak may be a contributor.
I suspect it is more likely a combination of sensors.

Rebuilt stock with composite head gasket, < 30 miles & <240 minutes running. No sensors replaced, all original.

I'm going to see about taking my AFR out of my car and hooking it up to the O2 to see what that shows.

Thanks for any directions, hints & pointers. Gotta love cars, still I keep saying it beats a car payment lol

 

[AJ'S 88NA]

Vac leak could cause it. Did you replace the hoses or are they 20+ years old?

 

[afofsupra]

We replaced any hose that had visible signs of wear, like cracked ends or cracked sheath when bent and any that were stiff. I think they all should have been replaced personally, I replaced all of them on my 90 corrado with silicone ones. Probably tell him that he needs to pick a few more feet of hose and just start replacing them.

Thanks AJ...

 

[supramacist]

Spray around your hose set up with starting fluid.
If you're leaking you'll know it. That's if you can keep her running long enough.
Sounds like maybe you can't.

It sounds to me like your ecu may not be picking up the signal such as it should from maybe the TPS. I say this because you described it as going hunting. And to me that says sensor, electrical.

The hoses leaking could cause odd idles surges.

 

[afofsupra]

Thanks supramacist! I was going to check the ohms on the TPS but his multimeter doesn't work without a fuse, go figure . I'll pick up a can of starting fluid on the way over there & a mini .315amp fuse (along with my multimeter). After this, I'm going to rebuild another stock na for another 87 w/ automatic. Have 2 complete 7mge w/ rod knock & 1 complete motor with burnt pistons (that head's gotta be warped!).

With SM's helpful group of knowledgeable folks, I'm quickly gaining an appreciation for the 7m motors. Combustion is combustion

 

[86yota]

Thanks supramacist! I was going to check the ohms on the TPS but his multimeter doesn't work without a fuse, go figure . I'll pick up a can of starting fluid on the way over there & a mini .315amp fuse (along with my multimeter). After this, I'm going to rebuild another stock na for another 87 w/ automatic. Have 2 complete 7mge w/ rod knock & 1 complete motor with burnt pistons (that head's gotta be warped!).

With SM's helpful group of knowledgeable folks, I'm quickly gaining an appreciation for the 7m motors. Combustion is combustion

dude i have been having the same problem with my 7mge i also rebuild it about 200 miles ago , it started right up and first time i had to adjust the timeing a little but it idles nice and smooth at 900 rpms then once i started driving it the "hunting" idling came back just like before i did the rebuild so far i have check and replaced all the vacuum lines i checked the tps even replaced a water temp sensor, still cant figure it out if u have any luck please share i hate having to keep a foot on the gas when i come to a light. lucky its a 5spd.

 

[afofsupra]

Yeah 86yota, I'm told it was like this from the beginning, but not quite so extreme. I've triple checked the TPS & ISC and now I'm thinking about switching the O2 sensor since it doesn't check out according to TSRM (no voltage bounce across E & VF on check connector) it holds steady at 2.2v.

 

[supramacist]

This is only the tip of the top guys.
It's going to get alot worse before it gets any better.

 

[afofsupra]

This is only the tip of the top guys.
It's going to get alot worse before it gets any better.

ouch! Maybe I should run now, the corrado is temperamental enough!

 

[86yota]

I dunno see the last few days i have been driving her differently instead of just popping out of gear when stoping i have been idling down real slow keeping my foot on the gas just lil and letting up at 8-900 rpms and it stays right there until i hit the throttle again, which i know it causing vacuum , which i why i was believing that it was something to do with vacuum control or something maybe ill figure it out. like i said i rebuild my engine....it has to be something old that i swapped over.

 

[BLACKCAT]

Have you cleaned the idle speed control valve?

 

[86yota]

no i have not but i plan on hunting it down doing so thanks for the advice ill let u know how that goes....iam off today