Jerking from time to time, especially on cold engine - Kia Forum
 
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post #1 of 2 (permalink) Old 07-12-2019, 02:02 AM Thread Starter
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Jerking from time to time, especially on cold engine

Hi. I really need your help.

I have Kia Sportage 2 generation, diesel 2.0l, 4wd 103kw, 140KM. From time to time car jerks in one of 2 ways. When the engine is cold it jerks really bad. Whole car is jumping forth and back. It jerks somewhere on the 2nd gear, 3 - 5 times. Usually just after starting the trip. After that it rides smoothly like a brand new car, just like nothing happen. Warming car on idle by 1 - 2 minutes doesn't solve the problem. Another possibility is that the engine is hot. Then the jerking also takes few seconds but it's so delicate only the car's owner can feel that. The jerking is rather rare. It is like that for 1 year. No other symptoms. Car is serviced yearly and in very good condition (yet it is 10 years old). No OBD error codes. I already was few times at car mechanic but they have no idea as there are no OBD codes. They were even amazed by how nice the car behaves looking at OBD data.

I bought OBDLink MX to catch the moment when the car is jerking.
Below is data from OBDLink. Not much as obdlink doesn't report many data for Kia. But I did catch the jerking ("slightly" one) on hot engine. I put data below. Can anybody help me to interpret it?

I can see that MAF sensor reading is dropping greatly thus it is the main suspect. Also 'Intake manifold absolute pressure' is dropping nearly by half. Also Boost is falling. The egr error is jumping up and down but when I check on the other OBD dashboard then I see that average egr error is ok (2-6%) and no car mechanic complained about egr error on their scanners so I guess it's rather some problem with obdlink (however on KS 4 generation obdlink catches much more steady and sensible egr error values). I already cleaned MAF sensor but it didn't help. I clean it only from one side. Should I buy a new MAF sensor but on the other hand all those sensors are coupled tightly so maybe much better would be if I found some better car mechanic? The problem is that jerking is too rare and usually happens when car is on road. One more thing, sometimes I hear single misfire when the engine is on idle but it's even rarer than jerking. Car has only 123000 km.

Well... it can be MAF sensor but also MAP sensor or EGR I guess (Intake manifold absolute pressure drops greatly also). Besides if that would be a MAF sensor shoudn't such hesitating/jerking occur more often? It happens something like 1 per 10 trips and also usually only once per trip and on cold engine rather. Once it well warmed up then it can work perfect up to the end of the day. One more thing that can be related or not. When I start the car initial exhaust gases are quite smelly. Once the engine warms up then they "smell" ok (clear). This appeared also some time ago like 1 year.

So to sum up
- jerking on attached excel happens on orange rows - 1835 second
- I suspect EGR (because jerking is rare and usually single per trip)
- Looking at OBD I suspect MAF sensor (however if that would be MAF or MAP then jerking should repeat many times during single trip)
- car mechanics negates EGR fault idea for some reason... maybe due to the car is starting very well and the exhaust gases are transparent
- initial exhaust gases stinks, they smell ok after engine warms up,
- happens since 1 year and 20 000 km, it has started to appear more and more but very slowly
- car serviced yearly, all filters & oil changed
- attached excel presents jerking on a steady ride, once I was approaching the junction, thus I was a bit engine breaking - this gives good insight as RPM are quite steady. I also has an excel when jerking happens on cold engine but then nearly every parameter jumps up and down and due to that it's rather useless as too many variables are changing

Please help.

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post #2 of 2 (permalink) Old 07-12-2019, 02:19 AM Thread Starter
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Excel is too big so I put it on the outside service.
send.firefox.com/download/10cf4b2929e00416/#bADo33Jj1_i5QXkeQHaIPQ
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