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You never mentioned whether or not the Montana generated a diagnostic trouble code? Have you checked for vacuum leaks just to be sure? One final question…Did you remove the plenum to access the EGR valve? Hope you are making progress.
..You never mentioned whether or not the Montana generated a diagnostic trouble code? Have you checked for vacuum leaks just to be sure? One final question…Did you remove the plenum to access the EGR valve? Hope you are making progress.
..Hello, I’m pretty familiar with this engine. I don’t know that a relearn procedure would be necessary. The PCM should revert to the pre programmed settings for the IAC and TPS and adjust accordingly. I could be wrong here.
Here is an idea or two, followed by a question.
First, you may have a simple vacuum leak. This can cause high idle. Check your vacuum line from the pcv valve line where it mounts into the top of the front valve cover. Then check it where it routes to the purge solenoid (just behind throttle body and in front of EGR valve). Also, check the vacuum line at the fuel pressure regulator and where it routes to the MAP sensor at the back middle of the plenum. Don’t overlook the big main vacuum line coming into the plenum from the brake booster. Eric has some helpful videos about how to check for vacuum leaks.
A second suggestion would be to purchase a simple vacuum gauge (if you don’t already have one) and see what the reading indicates. There is a vacuum test port at the right front of the plenum near the fuel pressure regulator.
Did the high idle originally start out of the blue, or had you done any other work to the vehicle lately? Did either the IAC or TPS throw a diagnostic trouble code?
Best of luck. Keep us posted. tomatofarmer1
Hello, I’m pretty familiar with this engine. I don’t know that a relearn procedure would be necessary. The PCM should revert to the pre programmed settings for the IAC and TPS and adjust accordingly. I could be wrong here.
Here is an idea or two, followed by a question.
First, you may have a simple vacuum leak. This can cause high idle. Check your vacuum line from the pcv valve line where it mounts into the top of the front valve cover. Then check it where it routes to the purge solenoid (just behind throttle body and in front of EGR valve). Also, check the vacuum line at the fuel pressure regulator and where it routes to the MAP sensor at the back middle of the plenum. Don’t overlook the big main vacuum line coming into the plenum from the brake booster. Eric has some helpful videos about how to check for vacuum leaks.
A second suggestion would be to purchase a simple vacuum gauge (if you don’t already have one) and see what the reading indicates. There is a vacuum test port at the right front of the plenum near the fuel pressure regulator.
Did the high idle originally start out of the blue, or had you done any other work to the vehicle lately? Did either the IAC or TPS throw a diagnostic trouble code?
Best of luck. Keep us posted. tomatofarmer1
It’s been a while since I updated this post. The car was at my friend’s shop for several weeks as he did some trouble shooting between paying jobs. He finally exhausted his efforts trying to find the misfire and turned it back over to me. I’m happy to report the mystery misfire is fixed!!!! I discovered the problem was caused by an after market harmonic balancer. Hallelujah!!! I made a Youtube video to help anyone else who may encounter this issue and P0336 DTC code. I’ve attached it below. Thanks to Eric and all of you who offered support and advice as to potential causes. I received much encouragement and learned through this process. Take a couple minutes to check out my video…not much to watch, but hopefully it will help someone who faced a similar challenge.
It’s been a while since I updated this post. The car was at my friend’s shop for several weeks as he did some trouble shooting between paying jobs. He finally exhausted his efforts trying to find the misfire and turned it back over to me. I’m happy to report the mystery misfire is fixed!!!! I discovered the problem was caused by an after market harmonic balancer. Hallelujah!!! I made a Youtube video to help anyone else who may encounter this issue and P0336 DTC code. I’ve attached it below. Thanks to Eric and all of you who offered support and advice as to potential causes. I received much encouragement and learned through this process. Take a couple minutes to check out my video…not much to watch, but hopefully it will help someone who faced a similar challenge.
Hi 13aceofspades13,
I thought I would address a couple of your questions as this post really is long. Maybe I can summarize so future viewers can be spared the pain of reading my small novel here.
Back in January, due to the common issue of coolant in the oil, I went into the engine. The following items were addressed/fixed: timing chain and sprockets, new harmonic balancer, head gaskets, heads pressure tested at machine shop, valve seals replaced, intake manifold gaskets replaced.
After the repair, I had a combination of issues, including a loping idle and misfires on a few cylinders. Some improvement was made by addressing unmetered air issues in the intake and changing the o-rings on the fuel rail and injectors.
After all vacuum related issues were addressed, I still have a misfire on cylinder number 2. This has been present since the repairs were made, but not before.
The engine only once threw a code, P0336. The following has been addressed. The 24x and 7x crankshaft sensors were replaced as well as the camshaft position sensor (all AC Delco OEM). The spark plugs have been replaced with AC Delco iridium plugs.
To address the possible misfire cause(s) in this cylinder, the fuel filter, spark plug, spark plug wire, coil and ignition control module have all been tested (either replaced or temporarily swapped out). The misfire is still present.
The vehicle is now with a very good mechanic friend for further trouble shooting. I offered your suggestion about the possible demise of the fuel pump. He disagreed, saying that if that were the case, it would likely show up in more than one cylinder. Thanks much for your interest and input. I’ll wait until I have some more solid information before updating my post again.
Hi 13aceofspades13,
I thought I would address a couple of your questions as this post really is long. Maybe I can summarize so future viewers can be spared the pain of reading my small novel here.
Back in January, due to the common issue of coolant in the oil, I went into the engine. The following items were addressed/fixed: timing chain and sprockets, new harmonic balancer, head gaskets, heads pressure tested at machine shop, valve seals replaced, intake manifold gaskets replaced.
After the repair, I had a combination of issues, including a loping idle and misfires on a few cylinders. Some improvement was made by addressing unmetered air issues in the intake and changing the o-rings on the fuel rail and injectors.
After all vacuum related issues were addressed, I still have a misfire on cylinder number 2. This has been present since the repairs were made, but not before.
The engine only once threw a code, P0336. The following has been addressed. The 24x and 7x crankshaft sensors were replaced as well as the camshaft position sensor (all AC Delco OEM). The spark plugs have been replaced with AC Delco iridium plugs.
To address the possible misfire cause(s) in this cylinder, the fuel filter, spark plug, spark plug wire, coil and ignition control module have all been tested (either replaced or temporarily swapped out). The misfire is still present.
The vehicle is now with a very good mechanic friend for further trouble shooting. I offered your suggestion about the possible demise of the fuel pump. He disagreed, saying that if that were the case, it would likely show up in more than one cylinder. Thanks much for your interest and input. I’ll wait until I have some more solid information before updating my post again.
Are you sure those are the transmission cooler lines versus the power steering lines that are routed just behind and underneath the radiator? If so, it could be power steering fluid leaking from the power steering pump/lines from above. This would be passenger side and near the engine mount on the subframe. That’s where the power steering lines bracket is located. The transmission cooler lines actually connect to the radiator itself. Send us a pic if you can. Best of luck….
Are you sure those are the transmission cooler lines versus the power steering lines that are routed just behind and underneath the radiator? If so, it could be power steering fluid leaking from the power steering pump/lines from above. This would be passenger side and near the engine mount on the subframe. That’s where the power steering lines bracket is located. The transmission cooler lines actually connect to the radiator itself. Send us a pic if you can. Best of luck….
I respect and appreciate everything you guys share from your wealth of experience. While I would rule nothing out, this misfire was not present until after I went into the engine due to the common intake manifold gasket issue. My first post summarizes what I did in January. So if it is mechanical, it’s likely something I caused during the repairs. This one may truly remain a “mystery misfire” until the end…
I respect and appreciate everything you guys share from your wealth of experience. While I would rule nothing out, this misfire was not present until after I went into the engine due to the common intake manifold gasket issue. My first post summarizes what I did in January. So if it is mechanical, it’s likely something I caused during the repairs. This one may truly remain a “mystery misfire” until the end…
Thanks much Eric; I did notice that my post was much longer than most. I appreciate the freedom to keep going. I wouldn’t rule anything out as this point, but when I did the work back in January, I replaced the timing chain and sprockets. The new one had less slack than the old and lined up nicely. I’ll see what my mechanic friend finds out soon. I’ll be sure to post it. Also, I’ll pass along you suggestion here. The timing chain cover is unfortunately sealed as it does not utilize a distributor. Thanks for your interest. I have an Aunt who lives in Adams county Ohio, not far from you. She owns a huge farm…would love to come to the “meet up” in July sometime…