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HELP me fix a high idle issue 1300RPM+?

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Old 07-28-14, 04:51 AM   #1
technol
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Default HELP me fix a high idle issue 1300RPM+?

Hi guy's I have a 1991 LS400 that is giving me problems with a high idle. 1300RPMS

So far I have done the following:

1. Replaced EGR Filter/ Cleaned out EGR.
2. Cleaned IACV
3. Replaced IACV
4. Cleaned throttle body butterfly
5. Changed PCV:


6. Started tinkering with TPS.. It no longer idles at + or - 2000 RPMS but now a more manageable 1200-1300 RPMS. I have a new TPS coming in the mail today.. Any other possible ideas here?

My AC unit seems to randomly work also, I'm not sure if IDLE and A/C have anything in common here.
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Old 07-28-14, 02:20 PM   #2
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Ok so I replaced the TPS and still the same thing.. The car surges a bit when it first starts.. Any common source of vacuum leaks ? Or does this sound like a vac leak? Thank you all!
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Old 07-28-14, 02:26 PM   #3
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From what I've read this is normal when cold, mine does the same thing until it's hot and then the RPM lower to 600ish

Also new motor mount could help lower the surge.
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Old 07-28-14, 03:24 PM   #4
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Quote:
Originally Posted by technol View Post
Ok so I replaced the TPS and still the same thing.. The car surges a bit when it first starts.. Any common source of vacuum leaks ? Or does this sound like a vac leak? Thank you all!
Could be. Easy way to check though: throttle body/carb cleaner with the little hose ($6 tops at any auto store). Turn car on, spray around all hose openings and basically anywhere where air can get into the engine. If it idles up, you've got yourself a vacuum leak.

Check throttle cable as well. If it hasn't been adjusted to spec, that could be your issue right there. I'm not sure of the way that the engine bay is setup on the ucf10's but the throttle cable will be easily recognizable by a long twisted metal cable with a spring (more than likely) directly under or in front of it attaching to the throttle assembly (not the throttle body assembly). Should be near the throttle body though .
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Old 07-28-14, 05:36 PM   #5
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I worry about the ECT sensor keeping the resistance high even at the warm condition. In that case, the ECU judges the water temperature cold and it sets the idle RPM high. Use a 33 to 100 ohm resistor or a small bulb 2-5W instead of the ECT sensor and see the RPM drops.

Last edited by Yamae; 07-28-14 at 05:42 PM.. Reason: to add the way to confirm
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Old 07-28-14, 05:59 PM   #6
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Thanks for the replies! I did make a strange observation, there is a "dashpot" or adjustor of sorts with a screw located under the tps. I notice if i put pressure on said screw the idle seems to go to a normal 600-800 RPMS... is this a screw i can simply adjust? What does it do? Is there somewhere else I should be looking? If i adjust the TPS clockwise it just surges upwards. Right now idle is at 1100 with a weird surge at the intital start. Any ideas?

Thanks again for being such an awesome resource guys!
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Old 07-28-14, 06:06 PM   #7
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Quote:
Originally Posted by Yamae View Post
I worry about the ECT sensor keeping the resistance high even at the warm condition. In that case, the ECU judges the water temperature cold and it sets the idle RPM high. Use a 33 to 100 ohm resistor or a small bulb 2-5W instead of the ECT sensor and see the RPM drops.
Yamae,

I will go ahead and do this one just because it seems easy and worth wild! Thanks for the tip.. Any ideas on the throttle screw I mentioned in the above post?
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Old 07-29-14, 05:04 AM   #8
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Can anyone chime in as to what I may need to adjust? Thanks guys.. I think it has something to do with that screw / dashpot located under the TPS.. it almost seems like the throttle may be set incorrect?
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Old 07-29-14, 06:03 AM   #9
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Ok so I have attached a pic of the object in question? Located right under the TPS sensor, what is this and can I adjust it to fix my idle?

Click the image to open in full size.
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Old 07-31-14, 05:27 AM   #10
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+Bump any further guidance here guys?
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Old 07-31-14, 08:35 AM   #11
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I dont think that is adjustable. You might try a replacement? How doesthe vacuuume line look going to it?
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Old 08-01-14, 11:30 AM   #12
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So I let up some slack on the Throttle cable, and backed down on that screw on the dash pot and things seem much smoother, although it surges initially, and I am going to replace the Coolant Temperature Sensor based upon Yamae's comment today!
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Old 08-01-14, 06:44 PM   #13
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Quote:
Originally Posted by Yamae View Post
I worry about the ECT sensor keeping the resistance high even at the warm condition. In that case, the ECU judges the water temperature cold and it sets the idle RPM high. Use a 33 to 100 ohm resistor or a small bulb 2-5W instead of the ECT sensor and see the RPM drops.
I replaced the ECT sensor.. Same behavior... I have ECU caps on order, could this be related ?
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Old 08-01-14, 06:44 PM
 
 
 
 
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