Dads90

Well, after a New Years weekend of reassembling the intake, runners,plenum,fuel injectors,wires,distributor cap, rotor and adjusted the rocker arms, I finally got to run almost perfect. First issue, idled rough and missed at 1500 rpm. Thanks to noisy Bosch/Ford injectors I heard no ticking in the #5 injector. Closed the contacts on the harness connection with a small screwdriver and WALAH !! the injector is now firing and running better. Second issue, still wasn't right. Turned out #4 and #3 spark plug wires were swapped, DAH !! Running great now. Final issue, it sometimes idles great ( 600-700 rpm) and sometimes bad (500 rpm and less) it does flucuates, will start a new thread for suggestions, thanks to all the forum members who helped me thru this.

bogus

cool! Way to go!

As for the wacky idle, did you replace the Idle Air Control? The IAC controls idle... if it is sticky, or the ports in the TB all carbonned up, it would create issues.

Dads90

Thanks for the reply, Bogus. I will be checking the IAC tomorrow. The TPS voltage was at .52 tonight, had a brainstorm at 12:30 am and ran to the garage to check it. The GSM states not let the IAC come in contact with a cleaning solution. I did spray off the TB when it was off, not thinking about the IAC. Hope that didn't hurt it. Didn't submerge it or soak it, just knocked the grime off. How do you clean it up if you can't use solutions on it ? Maybe stay away from the electrical sdie ? Also, is there a gasket kit available for the TB ? Don't want to tear it apart without the gaskets on hand ?

RRT vette

I would check for vacuum leaks if the idle flucuates. Does it smooth out after closed loop or when the engine warms up say past 140*?

Most autoparts stores sell TB gaskets (~$4). Make sure it looks like the one you take off. They make a few different shapes. The IAC pintle and motor windings can be cleaned with TB cleaner. It won't hurt, just don't spray the electrical connection with the TB cleaner. Use CFC electrical cleaner for that if needed. When reinstalling the IAC make sure the tip of the pintle is no further than 1 1/8" from the tip of the flange.

Dads90

Does anyone know what is normal vacuum ? I get about 15.5 inches measured from the brake boost line. It shows a little late on the timing on this type gauge. All my lines look good and have checked been many times. Haven't given up on this issue yet. This car is clean. It sat for years and the engine compartment componets are very easily visible ( no grime, dirt etc.) The vaccum lines are still new looking. (not saying its not a possibilty, could be dry rot) Still exploring. The idle starts out good constant at 900 rpm. All long as it sets it says there. Drive it and it will sometimes drop to 500 setting at a light. When the temp rises it will start idling rough. One good thing, turn on the AC it doesnt affect it like it used too. It used to really drop the rpm's bad enough to cause it to almost diesel. Not now. Check the IAC today, and maybe replace the temp sensor while the TB is off. Stay tuned !! Thanks for the help.

RRT vette

On the L98 with a stock cam you should have around 17", I believe. Sounds like you've almost got this thing figured out. If the SES light is not on, it's just a guess at what could be causing the drop in RPM and rough idle, besides a small vac leak. Best thing to do would be to get the ECM on a scan tool to view all sensor function. Have you used propane or starting fluid around the vac lines to locate a leak? Have you cleaned the MAF with electrical cleaner?

Dads90

Well today, I removed the TB (so easy now its bypassed) and replaced the gaskets, cleaned out the carbon build up, and cleaned the IAC up. It had a lot of carbon build on the pintle. Gently scraped it off with dental tools and sprayed the end and spring area. It was short a milimeter on the length. Did pull barely to extend it. If it screws it up Ill just get a new one, just wanted to see if it made a differance. Started it up and it idled at 950 to 1000 rpm. Never idled down, remained there even when the car temp got to 230 degrees. At least it didn't idle rough, the vacuum was steady at 16 inches (almost there). I'm driving it to work tomorrow and road test it. Should the IAC be springy, easy to turn or push ? Mine seemed stiff, carbon build was dry and crusty.

RRT vette

The IAC should be a little difficut to pull and push with a wiggle. Did you reconnect the connector. At this point I would recheck timing with EST disconnected and set the minimal idle. Check TPS voltage at closed throttle and WOT. There are steps to take. If you need them, let us know.

Dads90

Connection is good. Will check to see if I can retract the IAC using the ALDL grounding method. I just dont think its moving as it is supposed to. Also the TPS voltage is only .52 . I can't move it anymore to get the voltage specified (.54) closed. Is this bad ? I drove it to work today and it ran good, only the idle issue. Is setting the minimun idle possible with my year ?

RRT vette

If you ground the ALDL, it will extend the IAC pintle fully. I would rather have a little over .54 than under.

https://www.corvetteforum.com/techti...D=55&TopicID=2

vader86 also had a good guide in his website.

Dads90

Replaced the IAC and TPS. Followed the directions on Vaders site exactly. Also followed the tech tips instructions as well. When I started the car it did idle at 550 rpm's. Thats were I would like it. But when I accelerated it dropped back down to 900 rpm's. Do I need to let it idle longer ? I sat in it and then reved it up about 30 seconds later. Thats where it presently is. Its late and I'm going to bed. I'll toss and turn all night thinking about this. The TPS is adjusted to .54 volts but it is turned so far up to achieve this setting I can't get the bottom screw in. Whats up with that ? Any help is always appreciated ?

rick lambert

If memory serves correct, the IAC will reset itself after a short period of driving. As for the TPS, have you checked the entire range, it should increase from .54 volts as you open the throttle (by hand) smoothly to about 5 volts at WOT, check your specs. Make sure the connections are clean and tight...some guys have found it to be simply the connection.

Dads90

Thanks, Rick I'll check the range. It's new, I figured it was OK. But anything goes now. There was probably nothing wrong with the old TPS. But I don't understand how to adjust the darn thing when it has small single holes for each screw and cant be turned no more than 1/16 of a inch. I'm about tear the wires pushing the voltage meter leads thru the insulation. I will try to reset the TPS with both screws attached. I'm going to go thru the whole process again to reset both IAC and TPS and maybe it will stay set.

RRT vette

Key on. All you need to do is loosen the TPS screws and move until the voltmeter reads .54v. Then screw the torx screws down. Open the throttle while watching the voltage. It should increase smoothly as the throttle plates are open. When you open the throttle plates fully (WOT), the voltage should read more than 4.0v and less than 5.0v.