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Throttle adjustment simplified

W

Wesdunns70t5m

Member
Joined
Oct 4, 2016
Location
Fort Smith Arkansas
So, today I went to try and adjust my throttle by the book with no success. I fought with mine for a while until I finally tried something, and my car seems very happy about it so far. I figured I would post this up here for anyone's criticism or comments, and possibly to help someone out in the future. The best part about this method, is you don't have to block off the IAC valve

I'll try to keep this bread and easy to follow along
Step 1: remove linkage connecting throttle spool and actual throttle lever
Step 2: with the car warmed up and running, adjust the small set screw with a flat head screwdriver. My car seemed to be happiest around 900 rpms here
Step 3: adjust linkage arm so it will drop onto the ball socket without moving the throttle any
Step 4: loosen TPS screws, turn towards the driver side fully, and then back to the passenger side. I went slightly passed the point in which it clicks. Tighten screws after this point
Step 5: get in car and shift into gear. My rpms dropped to about 600 rpm here. Go for a test drive and make sure all is good

From me playing around with the adjustments, I found that if your throttle is too closed, you will have a very low idle. With it set too far open, I had a surging idle. Like throttle plate would be open and wanting to idle at say 1500rpm, every few seconds I guess the IAC would get mad and the idle would cut out to like 750, and then right back up to 1500 for a few seconds. It was rhythmic and predictable on when it would drop and catch.

After all my adjustments the car seems to be running better. My symptoms before checking all of this was that the car would start, idle, and run fine. My issue was whenever you let off the gas the rpms would drop to like 400 and sometimes stall. If it didn't stall the rpms would go back to normal and it would be fine again. I had no luck at all blocking off my IAC and trying to set everything that way. I will have to put more seat time in my car but so far it seems much better. Hopefully this helps someone in the future
 
This is all wrong.

You should have no control over the idle speed that is only set by the computer. With the IAC valve unplugged you are supposed to set the idle around 500 ish RPM. The idle will only surge if your TPS is not functioning or set incorecctly. It is actually just a switch and tells the computer the throttle is at idle. On regina and some LH2.4 it will have a WOT switch as well but that's not relevant.

You set the TPS so that it clicks just as you lift it off the stop and you adjust the linkage so it has full range from stop to stop with little slop.
 
Maybe you can answer my biggest brain itch, how do you know where the set the throttle stop set screw? I believe mine was all out of whack to begin with. My set screw was damned near screwed all the way in, keeping the throttle too open. The throttle lever and TPS switch were adjusted correctly at that point, but I believe my first adjustment point wasn't correct
 
Okay, don't adjust the idle from the throttle plate. Mine was out of adjustment and it's idling best now at factory settings. What injection is this? K-jet and LH2.0/2.2 both have a thumb screw for adjusting throttle speed and have their own procedure. It sounds like you have LH2.4 or Regina

Remove the linkage from the spool
Loosen the TPS first, the throttle plate may not allow full range of adjustment otherwise.
Loosen the throttle plate set screw, adjust so the screw is just touching the throttle plate arm then add a full turn.
Adjust TPS
Reattach linkage from spool and adjust if necessary

The factory settings are not why your car would stall. Trouble shoot it correctly and find the issue.
 
OVERDRIVE said:
Okay, don't adjust the idle from the throttle plate. Mine was out of adjustment and it's idling best now at factory settings. What injection is this? K-jet and LH2.0/2.2 both have a thumb screw for adjusting throttle speed and have their own procedure. It sounds like you have LH2.4 or Regina

Remove the linkage from the spool
Loosen the TPS first, the throttle plate may not allow full range of adjustment otherwise.
Loosen the throttle plate set screw, adjust so the screw is just touching the throttle plate arm then add a full turn.
Adjust TPS
Reattach linkage from spool and adjust if necessary

The factory settings are not why your car would stall. Trouble shoot it correctly and find the issue.
Click to expand...
Sorry, this is lh2.4

I'll give this a try when I get the chance, hopefully today. After making my adjustments, it did completely cure my stalling issue. When I ended up doing it my way it did end up landing the setscrew just barely touching the throttle, but it may not be perfect.

I've gone thru a bunch of troubleshooting when this was all going on. Checked O2 sensor, swapped AMMs (the one I'm running may not be "good", but it's exponentially better than the other one I'd swapped in. Throttle has been cleaned, IAC cleaned and confirmed it operates with 12v applied. I will try to make the adjustments per your instructions tonight and see what changes it makes.

I believe mine was way out of whack, and I ended up getting closer, hopefully following this j can get it totally dialed in
 
Followed your instructions with no change really. It's idling and running exactly like it was before. I must add, I did not disconnect the battery, so it might be a relearning situation

I'm still thinking something isn't quite right though. I know the computer is supposed to control idle thru the IAC valve at it aims to maintain 750rpm. Currently fully warmed up, I'm seeing about 900rpm in park. Once I shift it into hear that drops to like 550rpm. I'm not sure what would be the cause of this. Maybe the ECU? I do have an older 5xx (I think 561) that's got an old tlao chip in it. It is not a pink label, it's a white label. I've been considering installing my 967 ECU I've got. I don't have any aftermarket chips for it yet sadly. I'm not convinced (but very open to be) that swapping in a new, stock chip ECU would be wise, or just keep running my old ECU with an extremely early tlao chip.
 
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