B6 transplant revs up&down

[Biff]

OK , heres my first post to all , ended up putting a B6 into a 92 Festiva.
Pretty cool, easy install, using the B6 sensors, Air box, the engine revs up and down at idle all by itself only when engine has reached operating temp. The only thing is I'am still using the B3 ECU to control the system as I'am unsure that you can plug the B6 ECU I got with the B6 engine directly into the harness, because the B6 ECU is from an auto and mine is a std.?(3pin TPS std to the B6 4pin TPS)
When I unplug the temp sender on the intake manifold and unplug the IAC the engine runs normal other than it idles a little high ?
Any ideas, I have swapped temp senders which are the same, air boxes, etc , help ?

[batstiva]

As I understand it, the ECU controls fuel/air delivery, and the B3 Ecu managing the B6 will cause incorrect idle speeds due to incorrect fuel/air mixtures. Others on here, more knowledgable than I, may be able to correct me on this, but I believe, having read quite a bit about this, as I am looking into various swaps, that the B6 Ecu would likely solve the problems you have encountered. Any others with opinions on this??? :?:

[Biff]

Tks , I will keep watching, hoping , thinking , tinkering

[jeffdjeffd]

I have the EXACT same problem. I am fairly convinced it's the TPS. The 4-wire TPS of the B6/BP show constant variable resistance based on throttle position, and our B3 ECU only "sees" idle and WOT. What we both need to know is:

Is there a 3 position TPS that mounts directly to the B6/BP throttle body and is not vairable resistance - i.e. only has idle, open and WOT settings?

thanks,
jeff

[aithanmier]

i'd just swap in a b6 ecu...hell i think i have one around here somewhere...

[jeffdjeffd]

Won't help this problem. The Festiva has a three wire TPS, the newer ones are 4-wire. I suppose if you ran all new wires from the new TPS to the correct pin locations in the ECU it would work.

[Biff]

OK , so heres what I did. yes the TPS is different, 3 wire B3 and 4 Wire B6, so to make them the same I took the throttle body from the b6(because the IAC is integral with throttle body) and dissassembled it, welded a 3/8" bolt to the end of the throttle shaft and grinding the flat so it would accept the 3 wire original TPS.
It works fine as all the throttle body is, is a butterfly valve ! I'am kind of leaning toward the fact that the IAC valve is bad, when I take the original B3 IAC and touch 12 volts to it you can here it open and close, likewise if you blow in one pipe the valve definitely opens and closes.When I do this to the B6 IAC it does nothing ! .. so I took the guts out of the B6 IAC plugged any holes to the atmosphere plumbed the B3 IAC using a short jumper of hose between old and new, thought I had it, but engine still revs up&down when warm! possibly the voltage values are different between the two IAC's ? does the B6 IAC run on a straight voltage? , any way , still thinking,,, !!!

[Biff]

got it running like a top (how ever tops run?)
Turned out to be my TPS , needed to put it in the right spot , after modifying the auto TB with a shaft welded to the Butterfly shaft, cutting the flat spot in the shaft for the stock TPS to fit on it was hard to know exactly where it needed to be , any way , getting on to the paint stage.