Please help in fixing two very annoying issues. Idle&Speedo (1 Viewer)

Joined
Sep 17, 2017
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Hello, I am having trouble finding the cause of two very annoying issues. I have done a done of searching in this forum and a lot of the time I find people that have had the same issues I am having, but no one seems to follow up once they fix the issue. I hear by promise that when I fix these issues I will post what it took, so that some future soul has a good data point.

My vehicle: 1994 TLC USDM. about 160K original miles on the clock



Issue #1 My speedometer no longer works. It died about a month ago while I was driving and that was it. All other gauges and lights work. The car shifts perfectly and other than not knowing how many miles I have traveled or how fast I am going everything else in the cluster works.

Trouble shooting I have already done: Checked for voltage at the VSS, we are good, VSS has voltage. I also removed the VSS and tested its pulses and it is operating correctly. I have also check the wiring at the plugs near where the engine and transmission meet, all contacts are clean and securely connected. I have also inspected the wire harness where it passes the EGR and it looks good and intact.

With this TS I have a feeling that the problem is in the cluster itself. Has anyone had this issue before? Does anyone have a recommendation for a cluster repair place. I live in southern california but I would not mind mailing my cluster out to be fixed, the vehicle is not my primary.



Issue #2 It idles rough intermittently once warm. On a cold start the RPMs are elevated and the engine is beautifully smooth. After about 10 minutes of getting warm and driving around the idle will begin to pulse at stop lights almost like I have a big cam in it. If i just ever so slightly add throttle, say increase RPM to 800 it is smooth. The other annoying thing is that it's not 100% of the time, some times I will come to a stoplight once warm and it sits right around 600 as its supposed to and it idles great. Load does not really affect it, it will do it weather in gear or neutral. It never gets bad enough that the engine actually stalls.

Background: I had a BHG about 5k miles ago, I rebuilt the head after with all Toyota parts and really put a lot of love into it, it ran 100% perfectly for about the 5k miles after, I have done a recent oil sample to Blackstone and I have no sings of BHG now so it's not that. I also deleted the EGR and PAIR system about 10k miles ago and it ran great all during that time. My TLC does have a functioning CEL but this issue has never made it come on.

What I have tried to fix it so far: Even though the cap and rotor were in good shape I replaced those with toyota parts, i put in new plugs and wires and all 6 plugs looked perfect. I have also listened to each injector with a mechanics stethoscope and they all click in a healthy sounding rhythm. fuel filter was replaced when I did the head 5k ago. The intake pipe is a custom fabbed aluminum one i built with silicone fittings on each end that have been inspected (this has been like this for 10k miles). I have taken out and cleaned the IAC. It was pretty dirty but it cleaned up nicely. I also reset the ECU, this seemed to work for about 5 cold starts and then the issue came back. I have also inspected all vacuum lines and they were all replaced recently with new toyota vacuum line.

I am thinking it might be the IAC causing this even thought I have tried cleaning it. It is an expensive part and I don't want to buy it on a gamble. Please let me know what you think.

Please help, it's driving me crazy. Thanks in advance.
 

slow95z

Always parting 80s
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3,205
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Dublin GA
The trace on the back of the speedometer burns out. You can solder in a jumper if your skills are good enough.
 
Joined
Mar 2, 2015
Messages
113
Location
Knoxville, TN
Beware that the connector and wires can look great but still have continuity problems. The guy before me replaced the cluster in the my LX450 and it didn’t fix it. turned out that the vss ground that goes through the EC1 connector near the starter did not have continuity. It looked normal but when I opened the connector and checked it to ground on the pins it proved bad. With a gentle tug the wire came out of the back of the connector. So it was loose inside the connector no longer making good connection with the pin inside. I’m not the only person on here whose had that exact same issue with the EC1 VSS ground. It’s a big grey connector near the starter/firewall area.

Hello, I am having trouble finding the cause of two very annoying issues. I have done a done of searching in this forum and a lot of the time I find people that have had the same issues I am having, but no one seems to follow up once they fix the issue. I hear by promise that when I fix these issues I will post what it took, so that some future soul has a good data point.

My vehicle: 1994 TLC USDM. about 160K original miles on the clock



Issue #1 My speedometer no longer works. It died about a month ago while I was driving and that was it. All other gauges and lights work. The car shifts perfectly and other than not knowing how many miles I have traveled or how fast I am going everything else in the cluster works.

Trouble shooting I have already done: Checked for voltage at the VSS, we are good, VSS has voltage. I also removed the VSS and tested its pulses and it is operating correctly. I have also check the wiring at the plugs near where the engine and transmission meet, all contacts are clean and securely connected. I have also inspected the wire harness where it passes the EGR and it looks good and intact.

With this TS I have a feeling that the problem is in the cluster itself. Has anyone had this issue before? Does anyone have a recommendation for a cluster repair place. I live in southern california but I would not mind mailing my cluster out to be fixed, the vehicle is not my primary.



Issue #2 It idles rough intermittently once warm. On a cold start the RPMs are elevated and the engine is beautifully smooth. After about 10 minutes of getting warm and driving around the idle will begin to pulse at stop lights almost like I have a big cam in it. If i just ever so slightly add throttle, say increase RPM to 800 it is smooth. The other annoying thing is that it's not 100% of the time, some times I will come to a stoplight once warm and it sits right around 600 as its supposed to and it idles great. Load does not really affect it, it will do it weather in gear or neutral. It never gets bad enough that the engine actually stalls.

Background: I had a BHG about 5k miles ago, I rebuilt the head after with all Toyota parts and really put a lot of love into it, it ran 100% perfectly for about the 5k miles after, I have done a recent oil sample to Blackstone and I have no sings of BHG now so it's not that. I also deleted the EGR and PAIR system about 10k miles ago and it ran great all during that time. My TLC does have a functioning CEL but this issue has never made it come on.

What I have tried to fix it so far: Even though the cap and rotor were in good shape I replaced those with toyota parts, i put in new plugs and wires and all 6 plugs looked perfect. I have also listened to each injector with a mechanics stethoscope and they all click in a healthy sounding rhythm. fuel filter was replaced when I did the head 5k ago. The intake pipe is a custom fabbed aluminum one i built with silicone fittings on each end that have been inspected (this has been like this for 10k miles). I have taken out and cleaned the IAC. It was pretty dirty but it cleaned up nicely. I also reset the ECU, this seemed to work for about 5 cold starts and then the issue came back. I have also inspected all vacuum lines and they were all replaced recently with new toyota vacuum line.

I am thinking it might be the IAC causing this even thought I have tried cleaning it. It is an expensive part and I don't want to buy it on a gamble. Please let me know what you think.

Please help, it's driving me crazy. Thanks in advance.
 
Joined
Jul 17, 2018
Messages
65
Location
CT USA
I’ve been searching a similar problem with my idle at intermittent times and think I have it narrowed down to the NSS (neutral safety switch). Check my thread here for the pages on the FSM about when it controls idle. 96 LC usdm as well

 
Joined
Nov 13, 2002
Messages
580
Location
The Saratoga slums, CA
Did you take the IAC apart when you cleaned it?
Myself and several others here have had luck carefully taking the valve apart and cleaning and regreasing the worm gear inside. My valve tested fine according to the FSM but inside I found old dried grease that prevented the worm gear from working smoothly. I had symptoms similar to yours.
 
Joined
Feb 4, 2015
Messages
2,492
Just a question, but have you checked to see if you have any trouble codes stored in the ECM, and if there are any what they are.
 
Joined
Sep 17, 2017
Messages
55
Location
SOCAL
I fixed the rough idle!!!! Wahoo :bounce:

As promised here is what was wrong: It was the blanking O2 sensor plug. I replaced the O2 sensors about 9mo ago and overlooked them in my T/S, but sure enough I had a stored code of 26. I knew there was no way it was the sensor itself but sure enough when I pulled the connector apart that is on the bank that is on the furthest out side of the vehicle, water dripped out and the contacts were blue and corroded. I carefully polished the contacts with tweezers and steel wool and voila TLC runs great. Ive put 3 tanks of gas through her and not a single hiccup. What blows my mind is that it was running so rich that it must have been missing and yet no CEL stayed on (i don't even remember the 26 happening that was stored). If anyone wants to T/S this problem, its free and easy. Just unplug the O2 sensors and it will run with a CEL. If the car runs better than it did before you either have a bad sensor or connection.

Now to fix the speedo. I took my TLC on a big trip today and the cruise control worked great with no speedo so I am pretty sure its an issue limited to the inside of the cluster. if the wiring was bad I don't think CC would work. Right??
 
Joined
Mar 2, 2015
Messages
113
Location
Knoxville, TN
I would agree on the cruise that at least the wiring to the ecm are working. When I had a ground wire issue in the wiring of the speed sensor near the starter my cruise didn’t work along with the speedometer and odo. There are some troubleshooting tests to confirm if the instrument cluster is the problem in the FSM.

I fixed the rough idle!!!! Wahoo :bounce:

As promised here is what was wrong: It was the blanking O2 sensor plug. I replaced the O2 sensors about 9mo ago and overlooked them in my T/S, but sure enough I had a stored code of 26. I knew there was no way it was the sensor itself but sure enough when I pulled the connector apart that is on the bank that is on the furthest out side of the vehicle, water dripped out and the contacts were blue and corroded. I carefully polished the contacts with tweezers and steel wool and voila TLC runs great. Ive put 3 tanks of gas through her and not a single hiccup. What blows my mind is that it was running so rich that it must have been missing and yet no CEL stayed on (i don't even remember the 26 happening that was stored). If anyone wants to T/S this problem, its free and easy. Just unplug the O2 sensors and it will run with a CEL. If the car runs better than it did before you either have a bad sensor or connection.

Now to fix the speedo. I took my TLC on a big trip today and the cruise control worked great with no speedo so I am pretty sure its an issue limited to the inside of the cluster. if the wiring was bad I don't think CC would work. Right??
 

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