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Discussion Starter · #1 · (Edited)
Hello Everyone. I have been a following member for quite a while and have found the information in this forum very helpful. I have a 2014 CTD that i purchased in September 2013. I drive mixed 80/20 highway/city. I maintain the car well and its been very reliable for me, but I have experienced a few issues that i have been able to relate to on this site. Bucking (mild and severe) after coasting or light throttle, and a huge lag (almost a stumble) when hot in start/stop situations. I've also experienced several random hard downshifts. These problems first occurred when the car was about 1 year old (not that bad or often) and they seemed to improve after the first emissions recall. Shortly after the latest recall, the symptoms reappeared and gradually became worse.

Background/history:
107,000km
O2 Sensor replaced for P026C code - Mid 2015
DEF Tank Heater - Aug 2016
Emission Recall 15594 - Ran great after recall, but still got occasional P026C code
Emission Recall 17089 - Above mentioned symptoms re-appeared and gradually got worse

Two posts caught my attention: 15 cruze won't start or run, and Help diagnose bucking during regens. Since reading these posts, i have cleaned my EGR valve and the intake valve (throttle plate). Thank-you IndyDiesel for the write-up on cleaning your EGR valve - it went well, just as you described it. I did not replace the gasket plate but probably will if I service the EGR valve again. There is coolant behind the gasket plate and if you have any pressure in the cooling system, it will drip while the EGR valve is out (i had a small panic when i saw this). I have attached four pictures below. 1.) Location of EGR and gasket plate 2.) Intake pipe removed looking into throttle body 3.) close-up of the very gummed up throttle valve 4.) valve body after cleaning

I did the EGR first, about 5 days before i cleaned the throttle body. I noticed a significant improvement in fuel economy and acceleration. The valve was not stuck open, but it was not moving very free and it would sometimes bind up. I used brake clean and worked the valve back and forth with an attached vise-grip. I was pleased with the improvement in performance, but the car was still bucking, mostly first thing in the morning.

When I removed the intake pipe at the throttle body i pushed the plate closed with my finger and it did not release on its own spring tension, but would pop free after a second or so. I figured this could be the cause of the bucking. Cleaning this was much more challenging. I used throttle body cleaner sprayed on rags and a small plastic scrapper to do most of the cleaning. Since so much crap was falling down onto the bottom of the intake (just on the bottom where i could still see it) , i rigged up a small plastic hose (about 3/8 inch) connected to my shop vac to suck out all the carbon debris. What a mess in there - really disappointed to see. I think i could have removed the whole throttle body assembly as well which would make this much easier and allow access to clean further into the intake. Care should be taken to not spray any cleaners directly into the intake since any residual solvents would ignite and combust very different than diesel fuel, potentially causing significant engine damage.

So not sure why my intake got so gummed up. Are there any other reports on this? I've always used the proper engine oil and my UOAs have looked very good. I drive a lot of highway miles, but i could be a bit light on the throttle. All that stuff had to come through the PCV, so I may have to look at that further (catch can....ect.). I also find it interesting these symptoms came back after the latest emissions recall. I will be keeping an eye on the intake valve for sure. The car is running great again with fuel economy back up to near the best i've ever seen, and the bucking is gone, even during the regen it did today. I sure love this little car and hope this helps anyone having similar issues.

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Discussion Starter · #8 ·
Thinking I may try tackling this today (if its not raining), prior to our trip up north tomorrow. I'll probably just remove the throttle valve, though. That way I don't have to worry about what I use, and all the crap I cleaned out.
Good call. Curious how your intake looks. Great time to do this before a long trip!
 

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Discussion Starter · #12 ·
With my car being for last 25k miles being almost all highway miles, I am coming to the conclusion that driving our diesels hard on a regular basis might help. So the old saying drive it like you stole it might help more than I thought. The easiest way to do it is to run for a mile or two at 4000 rpm with the transmission in manual mode, maybe once a week. I think it could help, when dealer does a manual regen it is at 3000 rpm for an extended period of time, so I can't imagine 4000 rpm for a couple min would harm anything.
Agree - About a week before I cleaned my EGR valve, I tried running the car harder than normal. I was keeping the trans in manual gear 6 and letting the engine run full load up some moderate hills, letting off once I was too far over the speed limit. After a week of this I was seeing higher peak boost values. I think at full throttle full load, the EGR should be closed? So repeating this may have started to free up the valve. I took the EGR valve off as the performance was still inconsistent.
High RPM may be effective too, but it's hard to keep the engine at a full load at 3500rpm. The 2.0 CTD does not seem to be lugging in 6th gear at full throttle. I will make a habit of this on my drive home when possible.
 

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Discussion Starter · #24 ·
Niebs6.2---You quoted " I was pleased with the improvement in performance, but the car was still bucking, mostly first thing in the morning. " My car was doing the same even after cleaning the MAF,EGR and throttle body.Dealer finally figured out with the help from GM that the intake valves were caked with carbon.The fix is to remove the head and clean/recondition it along with cleaning the intake manifold (that part i'm assuming but the head is for sure).Mine was doing exactly what you describe,first morning start,stumbling and missing,worst when you first put it in reverse or drive and sit there with the brakes on.Fuel mileage was slowly getting worse,stumbling etc. goes away when engine warms up and runs smooth.No check engine light but dealer said they logged multiple misfire codes with their scanner,i guess those codes are stored but no check engine light.My cheap code scanner did not show anything.
Hey oreo382,
I've been following along on this topic since my initial post as my problem has returned. It has been getting pretty bad the last couple months. I've actually had it stall on me and when i went to crank it over, it sounded like it had poor compression - i suspect this is from bits of carbon breaking off and preventing a seal around the valve seat. So to me, your diagnosis makes sense. Too bad its such a big job (probably expensive too). Any suggestions on an intermediate fix ?
 
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