No check engine light, ruff idle problem

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Feb 4, 2015
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I've run into a intermittent ruff idle problem the past few days, but do to limited time i haven't had a chance to trouble shoot it yet. I'm working with a 1994 Land Cruiser. So far the problem seems to only cause the idle to drift up, and down between 650, and 475 RPM while in drive, with AC turned off. I've driven it far enough to make sure that it entered closed loop, and long enough for it to generate trouble codes.

As a quick check today i was able to Pull the rubber air intake tube off between the AFM, and throttle body looking for cracks, none found. Checked for any loose or broken vacuum lines, none found, checked for any plugged or leaking vacuum lines on EGR system, none found. Listened to see if all 6 injectors were clicking/opening, all 6 were clicking. I put a scanner on it late this afternoon, but no codes were found so i plan to dive into this more tomorrow.

Before i spend alot of time trouble shooting, do any other members have a quick source for this problem.
 
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Hi Rusty, listed in my post you'll find the answer to your question, i quote ''As a quick check today i was able to Pull the rubber air intake tube off between the AFM, and throttle body looking for cracks, none found" end quote.
 
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Oct 14, 2016
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I had a ruff idle awhile back and I pulled the intake tube and didn’t see any cracks/inconsistencies in the rubber but I put two coats of flex seal on it and viola it was back to normal idle must have been a small leak somewhere where the seams are:clap:
 

Shipwreck

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Nov 13, 2002
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The Saratoga slums, CA
IAC valve would be top of my list.
Testing procedure is in the FSM, however when mine was acting up it tested OK according to the continuity tests. After dealing with irregular idle for several weeks I went back to the IAC. I took it apart and found rust and dried grease on the worm gear inside. I cleaned it, regreased and my idle issue was solved.
 
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IAC valve would be top of my list.
Testing procedure is in the FSM, however when mine was acting up it tested OK according to the continuity tests. After dealing with irregular idle for several weeks I went back to the IAC. I took it apart and found rust and dried grease on the worm gear inside. I cleaned it, regreased and my idle issue was solved.
I'd second this suggestion. I was having very similar low idle issues like you described and after a good cleaning of my IAC it seemed to correct it. It's pretty easy to get to and cleaning it costs you next to nothing.

Idle Air control Valve cleansing pics

That thread talks about how tight the philips screws can be but I had good luck with a 3"+ long philips bit on a normal home impact drill/driver.
 
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I spent some more time today trouble shooting the truck and may of found the issue. Even though i found no noticeable vacuum leaks with all those small vacuum hoses. I decided after 25 years of use it would be a good idea to go ahead and replace all of them.

First a word of caution about buying replacement vacuum hose, the small hoses used on these trucks is 3.5 MM metric hose, most parts stores will want to sell you SAE 5/32 hose. Don't buy it, it won't fit tight, and you'll end up with vacuum leaks! You'll need at least 10 feet of 3.5 MM hose to replace all those little hoses, so plan on buying it in bulk.

Before i replaced all those vacuum hoses i hook up the scanner to base line the truck, i warmed the engine up and started watching the live stream date. After the engine went into closed loop it became clear that the right side O2 sensor was showing a problem with a steady 5 volt reading, so those cylinders were running lean. Plus that O2 sensor wasn't switching from rich to lean, it was just showing a steady lean.

After replacing all those small vacuum hoses and rerunning the truck in closed loop both O2 sensors now showed a constant switching between rich and lean. The voltage reading was now 2.5 volts which is considered optimal, and a very steady idle of 650 RPM. It looks like the source of my ruff idle may of been a combination of alot of little vacuum leaks. So it looks like 13 dollars of vacuum hose may of corrected the problem. I'll run it for a few days and report back.
 
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Here's an update, While driving home from the store yesterday the check engine came on, but only stayed on for about a minute before turning off again. Along with the check engine light the ruff idle has returned and the truck now has a trouble code, number 26.

So i started out my day today by doing a water pump, Dex Cool coolant flush, and fan belt change on my daughters car, let me tell you transverse mounted engines SUCK!. After getting that fun job done i jumped over to my Cruiser, the first thing i decided to do was pull all the plugs to check their condition, plus i took this opportunity to do a compression test too.

Below are a few photos of the plugs along with the compression test results. My factory service manual says that the compression should be 171 PSI with an allowable spread of 14 PSI. Looks like cylinder 2 is the only one i should be concerned with, but per the manual it's still within spec.

Now for the really fun part, after doing the compression test, and putting everything back together the truck now won't start. I guess i can just add the no start problem to the code 26, and ruff idle. All well I've got all day Sunday to work on it, Ha Ha.
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Jan 26, 2017
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Chattanooga, Tn
Here's an update, While driving home from the store yesterday the check engine came on, but only stayed on for about a minute before turning off again. Along with the check engine light the ruff idle has returned and the truck now has a trouble code, number 26.

So i started out my day today by doing a water pump, Dex Cool coolant flush, and fan belt change on my daughters car, let me tell you transverse mounted engines SUCK!. After getting that fun job done i jumped over to my Cruiser, the first thing i decided to do was pull all the plugs to check their condition, plus i took this opportunity to do a compression test too.

Below are a few photos of the plugs along with the compression test results. My factory service manual says that the compression should be 171 PSI with an allowable spread of 14 PSI. Looks like cylinder 2 is the only one i should be concerned with, but per the manual it's still within spec.

Now for the really fun part, after doing the compression test, and putting everything back together the truck now won't start. I guess i can just add the no start problem to the code 26, and ruff idle. All well I've got all day Sunday to work on it, Ha Ha.
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View attachment 1877661
View attachment 1877662
VAF issue (no no screws) or intake tube cracks? No start, did you hook everything back up to the battery and distributor after your plug removal?
 
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VAF issue (no no screws) or intake tube cracks? No start, did you hook everything back up to the battery and distributor after your plug removal?
I haven't touched the Air flow meter, or it's "no no screws" at all. I checked the rubber air intake tube by spraying it all over with Carb cleaner while the motor was running to see if the Carb cleaner effected the engine RPM which it would. Since there was no RPM change at all, there are no cracks or vacuum leaks in the tube.

When i pulled the plugs the only thing i removed was the air filter lid (without disconnecting the air flow meter electrical connector), rubber air intake tube, spark plug wire covers on the valve cover, plug wires, and the spark plugs themselves.
 
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Feb 4, 2015
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Update, after doing some troubleshooting I've found the cause of my no start issue. Checked for spark, no spark, so i tested the coil per the service manual it was bad. So i grabbed the extra coil i carry in my truck, plugged it in and the truck started right up. The bad news is, i still have the ruff idle, and the #26 trouble code.
 
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I think this will be my final update, I found what I'm sure is the source of my code 26 and ruff idle problem. While checking the Ohm's on each O2 sensor i found the right (passengers side) O2 sensor connector was full of water.

I'm sure all that water would cause all kinds of conflicting signals to be sent to the computer. After blowing all the water out of both connectors, i reconnected them, started the truck up, both O2 sensors were now working right, and the idle was rock steady at 650.

What i found, my truck is a 94 so I'm sure this will effect the 93 too, is the right side O2 sensor connector where it connects to the wiring harness connector is held in a vertical position. The problem with this position, even though the connector is supposed to be a weather tight connector, the bottom part of the connector is shaped just like a cup.

So any water that gets inside the connector will be held there, causing corrosion and never being able to drain out. What I've done to hopefully prevent this from happening again, I've turned the connector horizontally and tied it in place. This should allow any water that may get inside the ability to drain and dry out.
 
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