I have an idle problem with my 87 tpi conversion in my s10. The factory harness is being used along with all factory components with an exception of the alt (TBI style) and the air pump has been eliminated.
I'm trying to set the base idle but I can't get it below approx 650rpm before it starts to jump around and surge like crazy. The truck also stalls coming to a stop after driving and stalls going into gear. These problems only appear at temp. The diagnostic mode should eliminate the IAC as the issue but I'm not sure if the 3 iac's that I've tried have all been bad because they rattle as they are seating before unplugging them.
I get no codes, and only a faint gas smell from the fpr vac line, no wetness.
I can't see it being a vac leak as it only starts to do it at low rpm and if runs great driving. All ignition components have been checked and are very near new. Ect, and cold start switch resistance seems fine and has been cross checked to spares. Maf and ecm are new.
Any other ideas or something I'm missing?
Thanks for any help, Art

 

Setting the timing is not done in a diagnostic field service mode. When the engine is warm turn off the engine and disconnect the est and set your base timing to 6 degrees advanced. When you unplug the iac connecter in field service mode you will hear the iac clicking as its seated. After the iac is seated unplug the iac connecter and remove your jumper from the aldl and set your minimum idle speed. After the minimum idle speed is set you can set you tps feed back voltage. If you did not install or wire up a vss this will cause issues when coming to a stop with surging or dying.

 

Thanks. The timing is set at 6btdc with the est disconnected not in field diag mode. I'm trying to set the base idle now as the next step and this is where I'm getting the surging once the idle speed drops. And it is consistent, not sparadic.
The stalling coming to stop lights is a separate issue that was occurring before I began the idle adjustment. The vss makes sense for that as the speedo gear is... missing? but that is unrelated to the stationary idle issue. I thought the vss signal only controls trans lockup and without a signal, lockup is not applied. Shouldn't have anything to do with stalling as the iac should open as soon as the tps shows the correct value of tb closed .54v, no?
Would a weak charging amperage cause idle problems? Thinking maybe the TBI style alt charged less at idle than the tpi version.
Don't ask why the TBI alt or lack of speedo gear, I didn't build the truck just cleaning up the mess the prev owner made.
Thanks again

 

Low charging system voltage will cause change in your injector pulse width the effect is a stumble rough idle. With the iac commanded in and disconnected and out of field service mode if you have surging your egr could be slightly open.

 

Ok the charging issue to injector pw would make more sense.
Lets say the egr would be cracked open due to crap in the pintle, would that not cause a constant surge or stumble/low idle not a never ending up and down idle speed varying 300rpm maybe. Considering the egr is a positive back pressure needing more than a few hundred rpm, switch signal, and open throttle blades for vacuum to operate on its own. It has also been tested for vac bypass.
What about the ect sender, would that show correct resistance cold but intermittent at temp? I'd think it would either work or not.

 

The cts is a thermistor , it sounds like you are lean this could be bad injectors or bad maf as well. Have you hooked up a scanner to watch the o2 , maf, cts mat and tps ?

 

Fail

https://www.thirdgen.org/forums/post...740-post4.html
https://www.thirdgen.org/forums/post...475-post6.html
https://www.thirdgen.org/forums/post...362-post7.html
https://www.thirdgen.org/forums/diy-...cause-blm.html

https://www.thirdgen.org/forums/diy-...une-while.html
https://www.thirdgen.org/forums/diy-...-cell-4-a.html

 

Well that's good I learnt something. Not sure I failed thou...

I bought a new cts. Ill boil it and the current one and compare. The chart seems to be near the values at cold anyways.

No I haven't hooked up a proper reader to it yet. Might invest in one.

 

The point of the posts is
if you don't have a VSS input to the ECM then the ECM will not leave the idle fueling cell so you won't have correct ECM operation.
Ditto if the CCP ( canister purge ) is not deleted correctly

 

I know I hear ya. The canister is there and wired so that should still purge properly. Ill get to the speedo gear soon and that should fix my drivability issues. Like i said the vss and 2 pulse eye is all there but there no gear in the trans to spin the cable. The truck is an 88 and the engine/trans/ecm is 87 so they use the same 2 pulse style sender from what I've read. I must have skipped the part a about the other vss functions reading the jtr article before and just go stuck on the no lockup applied.
Now said that once I reset the ecm/codes and try to set idle before driving it, the ecm won't know that there isn't a vss signal so how could that affect setting the base idle and cussing the lope. Or again that's an unrelated issue with cts, maf, or o2... I did have a maf code 33 before and there some nasty relay wiring so I was going to upgrade to the newer style relay as I have them and a spare harness here. The code never came back but maybe the relay is acting up. The lope definitely feels like the ecm is adjusting something like fuel from one peak to another. It's that consistent.

 

What's the stock/normal operating temp for these cars. I think it's 195 thermostat and some say 200, some say 225? Maybe I've got my electric fans set a bit too high too. I jut wants to make sure the thermostat stays open. I know with my 2.8 camaro the stock Dan didnt kick on till 225ish, right at gauge redline anyways.

 

Ok, so I've got a bone to pick with tgo and corvette forums... Hmm let me get to that in a bit.

So after wasting a whole lot of time testing every sensor, wire, and vacuum line, I've got my adjustments made and the truck runs great. I did do a few useful things like getting the speedo gears and the vss working for the ECM, which was an adventure in its own due to no availability locally, and replace the shotty exhaust under the bed with Magnaflow out the back. My only glitch now is that sometimes the motor stalls out when I put it into gear when it's cold. Trans shifts pretty hard so I'm to sure if the shock load would cause that.

I want to say a big thanks for the vss info. It didn't affect my idle set but an instant night and day difference while driving.

So now to my bone, and don't get me wrong I love tgo, I think its the best thing for third gen owners out there and I've found tons of answers. I don't know enough about the vetteforums but the author says the procedure is right from the shop manual... I mean come on!
But... if we're gonna have tech articles they need to be correct and complete. If they're not, dummies like me are gonna end up in my situation again wasting time going in circles.

Here is what in talking about. I found the idle set procedure in a different thread on tgo as a picture insert from a shop manual. The shop manual has a highlighted "Important" with an exclamation to disconnect the est plug when doing the procedure. Neither sites tech articles even mentions it. Begin procedure, disconnect iac, disconnect est, start vehicle, disconnect ground... idled just fine right down to 400rpm, no bouncing. Perfect easy setup.

I don't know how to attach the picture for everyone now but for the future if someone is doing the idle adjustment look for the shop manual procedure and save yourself some possible, please.

So any ideas on the stalling is welcome and thanks for all the help so far.