PAIRA5S

I have an original 85 vette that I bought new. The stock throttle body does not have the second tube that you think is missing. In stock form the throttle body is not drilled through to allow this to be a vacuum port. I will have to look at the car to see where the vapor purge line connects to the engine. If it will help anybody, I will do that.

AGENT 86

I quickly skimmed through the posts so forgive me if this has been answered.
Where is the fresh air line from TB to passenger valve cover ?????
Have you tried disconnecting the IAC while your idle is at normal rpm. Doing this will take the ECM out of the "idle picture" any may help you find the cause of the surge.

jmrl98

My evap. purge to TB is on the driver's side, and goes to the T connection underneath, the pass. side tube missing goes to the pass. side valve cover breather on mine. Not sure how that could affect idle, if indeed no hole in the TB there.

davemack

Agent86, Thanks for joining the effort. I removed the hose that runs from the TB to the fitting that connects eventually to the pass side PVC for purposes of showing the vac fittings on the TB. It is in tact.

I have disconnected IAC and checked or reset min. idle several times. It does run considerably rougher with the IAC out of the picture and still hunts around for idle instead of holding steady.

davemack

I'd be grateful if you'd give it a quick look. My evap cap vac line attached to a T fitting that has what I believe is the EGR solinoid vac line coming into it as well. The vertical part of this T fiting then attaches to the fitting on the bottom of the TB.

It'd be good to know if yours is the same, since mine is an un-modded car, totally stock.

davemack

Sounds exactly like my set up, assuming the breather hose that attaches to passenger side TB connects to a fitting very near the AC unit, which then connects to a longer hose that runs pretty much the length of the valve cover to the PCV valve (located near the rear of the passeneger side valve cover).

So, it appears the "missing" vac port on the passenger side is not an anomoly, but rather just a different design than the later TPI models.

davemack

I'm off to Sears to do my shopping. I'll get a mityvac, FP guage and a better quality dmm. I bought a $15 dmm from Sears a while back, but never got it to give me a .xxx readout so I could set my TPS (wound up driving it to a Car X store to have TPS set).

When I get back, I'll re-set min idle with EST disconnected and see what happens. Back on in an hour..

davemack

Okay fellas, I've just bought a mityvac, FP guage and new dmm. Bump to my man goldeneyevette for finally getting me into the store to make the investment. I figured all of this stuff would cost at least a couple hundred buck if not more. Final tally - $110.

Need to give up a second bump to kopbet89c4 - the guy has poured it out in getting me to this point, sent pics and gave lot's of useful advise. Fantastic CF bro if I ever saw one.

Third bump goes out to Bruce Witherspoon, who has graciously offered me a working ECM from an 85 he's building to race at a near give-away price. You guys gotta check out his pics - unbelieveable. Can you say wheelie power??

Now for the hard part, how do I go about doing the necessary tests? I do own an FSM, so if anyone wants to point me there, I can try finding the relevant section. One thing about the FSM, it assumes you know what the heck you're doing. When will they release the "FSM for dummys"??

davemack

Just checked FP. Here is data:

Key in run position, but not running: 34 psig
Start-up: 31 psig
Running; steady at 31 psig, 150 F op temp
Shut down: 24 psig @ 1 minute, 20@2, 19@3, 14@5

Holds steady at 31 psig while running at "normal idle" - 700-740 rpm.

Revved engine (myself for once..) to 1400 rpm for about a minute and a half - released acceperator - idle dropped to 400 rpm for a second, then moved back to 540 rpm. FP dropped to 28 psig briefly, then back to 31 psig. Some light gray smoke emission, smells rich. 170 F op temp.

Idle smooths out at 630-660 rpm, 175 F op temp, FP steady at 31 psig, light smoke present still, smells rich.

Idle still smooth at 670-680, FP 31 psig, 180 F op temp, light smoke, rich smell.

Idles still smooth at 680-720, FP steady at 31 psig, 197 F op temp, light smoke, rich smell.

Test ran for about 15 minutes from start to finish. Thoughts?

davemack

No ideas? It figures; I'm ready to roll and nobody's on-line. Standing by..

One question; I'm planning to re-set IAC. I've read here (but see no reference to it in FSM or haynes manual) that I should disconnect EST. Can't figure out where it's at. Is it the clip-on style plug on the driver side of the distributor cap, or the plug that is kind of buried under the spark plug wires and lodged between dist cap and firewall on driver side? If the latter, how do you disconnest the plug? Don't want to break the locking cap..

Also, checked PCV - plenty of vac draw. Removed air hose from breather tube on pass side of TB - didn't make much difference in idle performance, even when I left the vac fitting on the tb wide open. It also is pulling good vacuum in that hose. Pulls quite hard (builds up vac draw) if I hold my finger over the end.

davemack

Mikey - I bought a mityvac, but don't know how to measure my vacuum draw. Where do I hook it up? Do I pump and watch for decrease in pressure, or do I hook it up and see how much draw is present? And, where do i hook it up? Is it one single point, or do I move it from fitting to fitting and measure vacuum draw or holding ability?

If possible, pls. elaborate on your advice. Thanks!!

AGENT 86

EST wire is a single tan wire with the connector being beside brake booster (engine side). You only adjustment you can do to IAC is be sure it is not longer than 1 1/8'' (from gasket to pintle end) before installing. After installing the IAC, the ECM will reset the IAC the next time the car is started.

davemack

Located EST. Thanks for that.

RE: IAC pintle length at install, I didn't read that until after I installed the IAC. I just pulled it out and measured it - it was at about 7/8 of an inch. re-set to 1 1/8 and re-installed. re-set IAC (didn't disconnect EST - might do so tomorrow if idle starts jumping around again).. Seems to be running better - idle varied from 690-710.

Also checked EGR - had to break in that new mityvac - held vac >20 seconds, so it's good. Plugged off EVAP canister and re-set min idle at 600 rpm as suggested by kopbet89c4, running just EGR solinoid on vac line under TB. Seemed to reduce rich condition somewhat. Very good.

That's where I stand. Right now, it's looking good. But, I've been there before, then the return of the "yips". But, I'm hopeful. More to follow tonight.

Thanks again Agent86, kopbet89c4 and goldeneyevette. I'm really grateful for the help. Heck, I'm thinking about recomending you guys for next years "Corvette Fever's 100 best mechanics". You've gotten me further than 2 of their current top 100!!!!

davemack

Took the car out for a drive this evening. Kind of the same old same old..

Started out idling great - 700-710 rpm. Perfect. Drove about a mile to drop off my child at a friends house. Pull up, car idles steady at 1200 rpm and won't kick down when I tap the pedal. Drive off, at next stop idle resumes at 690-710 rpm. Drive 10 more highway miles and car starts to idle at around 640-670. Still not so bad, but typically unsteady.

Start the drive home and the car idles pretty good, about 700-710. Stop at the video store, come out and car idles at about 630-670. Drive it home and it idles at around 690-710 when I pull up to the driveway, put it in reverse and back into the garage and it's idling at 630-660 again.

Oye. Can't win for losing. The saga continues...

PAIRA5S

I checked the vacuum lines on my stock 85. The difference that the 85 has, compred to the diagram that was in an earlier thread sent by
kopbet89c4 is minimal. The line running from the purge cont solenoid is teed into the line running from the pcv valve to the intake manifold. and the bottom fitting on the tb does not exist. Everything else is basically the same. I hope this helps

rick lambert

typically the first things you'd want to check for a surging idle are vacumn leaks and IAC. When your mechanic had his scanner hooked up he probably watched the IAC counts (or steps) and since you have a new IAC I'd probably eliminate that from the equation. Sounds like you've really taken time to check for vac. leaks too, so if your sure I'd move on. You said you have a new coolant temp. sensor, I'd put that in! Have you checked the voltage at the TPS? if not we can walk you through it.I need to go back and read your last post, because the idle seemed to be much better.

All but the one event at 1200 RPMs, it seems like your getting there....check the voltage at the TPS, follow the FSM for this.

davemack

Will do. I did have it checked recently and it was spot-on at 0.54v. But, things change. Another kind of wierd thing - when I had the IAC diconnected and the EVAP canister plugged off, car was no longer running rich. With the IAC re-calibrated and set and EVAP still capped off, burning a bit rich at idle, but better than when EVAP was still connected to TB.

I'm wondering a lot about the ECM. I bought a used one from another CF member and will try using that one when rec'd.

But, first things first. I'll hit the TPS here in a few minutes. Thanks for the help, Rick.

kopbet89c4

If your car still idles high, your throttle body plates could not be closing all the way. They'd probably sometimes hang up on the rough dirty walls of the TB. That would probably elevate your idle a bit.

Clean out the dirt in the TB first, lubricate the inside of the plates with WD-40 and get back to us.

davemack

I did completely spray the TB with TB cleaner before I replaced the IAC. It was also sent out for a re-build last July, so it got the full soak treatment. There was very, very little on the back side of the throttle plate, but I wanted to be sure that wasn't the issue. After spraying/wiping everything down (gave it about 45 minutes in the sun to dry before I installed IAC, made sure none of the cleaner touched the TPS) I put some mobile 1 in the center dip under the TB top plate to lube the plate shaft, but didn't lube the inside of the plate area. Will spray a quick shot of WD40 on both inside shaft ends.

Thanks again for the idea.

rick lambert

When you check the TPS not only check at idle but also at WOT, you can do this without the car running..just have the key to the on position...at WOT the voltage should be above 4 volts, then close the throttle...slowly open the throttle to WOT and observe the voltage reading, it should increase in a linear fashion, if it sticks, jumps or falls off the TPS could be failing.And, since you have it, I'd replace that coolant temp sensor.