[Vid6639]

The AC jerk is back on my car with a bang after the service. The service guys have messed something up. It jerks like mad now. I can't drive it with the AC on. The ECU was also reset.

They also did the throttle body cleaning but still no use. Tomorrow they check the plugs and coil.

[Gansan]

Originally Posted by paragsachania

I took the wheel again and started driving in peak traffic with AC On and in my driving style. After 20 minutes the difference was evident. The car was moving smoothly through the traffic in lower speeds. I advised him to develop this habit especially if the drive is through city at low speeds and load of the AC. I hope it gets better.

Well, back to OT then! Can you please elaborate about this driving style? It may be useful for Alto owners especially.

[paragsachania]

Originally Posted by Gansan

Well, back to OT then! Can you please elaborate about this driving style? It may be useful for Alto owners especially.

Gansan,

An understanding that you can always use all the gears in city driving without any load on the engine (5th at a few places if required) will be good enough here. As a matter of fact, once you adapt to this, you will master the art of ensuring that you dont unnecessarily pull through through the lower gears at high rpm's. You'll be able to make that perfect judgement with practice.

Usually, I use the first gear only to gain that momentum from stop and I am in second even before I hit the 10kmph mark, effortlessly and without a jerk or a knock! Most of my city driving, even if it is bumper to bumper (but moving) is in 3rd gear and I ensure that I never abruptly depress or release the throttle.

You may notice that when you are driving with the aircon on and are planning to slow down, if you release the throttle abruptly, there is 110% possibility that there will be jerking. Here, the throttle must be released as gently as possible so that you dont even feel that slowing down effect and thus no jerks as well. The Aircon running at a specific engine rpm will put the engine under stress if it drops suddenly and hence the jerk.

Same applies to depressing the throttle after changing gears. I've seen many clutching and changing gears and wait for a second before revving which actually lets the car loose that seamless momentum and after which if throttle is applied, there is again a possibility of the jerk. I usually start accelerating the moment my foot is off the clutch pedal after a gear change.

Again, if the speed is too slow to move in a particular gear, the jerks would be obvious and it is better to move to lower gears.

@vid6639's,

It is more likely the spark plugs. And after the ECU was reset, was the car run for a while under the normal everyday driving conditions so that it could read the driver inputs and map things accordingly? I think you drive the car for a day or two and check if the problem is still evident.

Unable to drive with the AC on is definitely an issue to look beyond the topic (Especially after the service).

[Gansan]

Thanks! I will try to adhere to that. My Alto was registered yesterday and I took it for a short drive afterward. Found no issues with the jerking, though the pick-up was (expectedly) sluggish with the A/C on. Could not follow your advise of seamless de-clutching / acceleration though. There was a slight lag between the two, but then I am driving after a gap of almost a decade. I have driven a car during this period very very infrequently. Hope I will get my touch back very quickly! I am taking delivery today.

[Vid6639]

A very strange solution to the problem.

During the service, they had cleaned the throttle body and my suspicion was towards that.

Farhan suggested I pour the OWS 360 and go for a high rev drive to clean out the injectors and that may remove the jerks. Tried it but it was as bad. The car was not drivable with the AC on and continued to jerk.

Drove to Surakshaa Electronics city and told him to do whatever it takes to remove the jerks. Went for a trial and the service guy was still clueless. He then cleaned the throttle body again, cleaned the spark plugs adjusted the plug gaps and cleaned the plug cables. We then connected the TECH-2 scanner to see if there was anything abnormal. No error codes observed, so we went for a short trial again to see if any error codes would pop up when the car jerks. After spark plug cleaning, and setting the gap, the jerk actually increased and it was horrible. The car was more horse like than car like to drive. TECH-2 didn't show any error codes even when car was jerking.

Next we decided to change the plugs and try. He put another set of used TVS champion plugs and the jerk reduced but only a little. It was difficult to replicate the jerk but it kept jerking once in a while. I remembered Farhan having suggested to check the ignition coil. Got that checked and it seemed fine. Alto uses a single ignition coil and is distributor less ignition.

Our diagnosis was that the electrical system was weak or some grounding issue. When the AC was on, there would be a heavy load on the electrical system. When you lift off the accelerator, the voltage would reduce which would mean lesser current for the spark. A weak spark would cause the jerking.

Next we decided to put in new better plugs. Replaced the TVS plugs with new NGK plugs and went for a drive. Voila!!! The jerking completely vanished. With the AC on, the idling was more stable and there was no more jerking. It just completely reduced. A better plug meant stronger spark and even when the voltage dropped the superior plug was able to give a strong enough spark and prevent the jerk.

Now the question arises why did the jerk appear only after service and it wasn't there before. During the service, the spark plugs were removed, cleaned with sand paper and gaps adjusted. Most probably they were damaged when cleaning or when the gap was adjusted. The gap might have been lesser than spec before making it easier to produce a spark even under load. The new gap was set to spec but was too high and would cause the jerk.

I'm still testing all parameters of the car to make sure that this is the definite cause. If the jerk appears I know the next thing is to check the ignition system and the coil pack.

Now the car is absolutely flying. The effects of the OWS 360 and oil change are now clearly visible. The car sounds much much better/smoother and is an absolute joy to drive. My dad blasted me the day after service as the car was worse to drive compared to before service. After the new plugs and OWS 360 he came and asked me what modification I did this time as the car felt much better now.

[gpa]

Vid,

An informative read. Its a strange problem, like you mentioned, but, am glad the change of plugs was able to sort out the problem. Do let us know if anything develops further after your checks.

[Gansan]

@Vid
Glad you got rid of the problem and the car is fine now.

I also felt slight jerks a couple of times yesterday and today.It was noticeable in first and second gears, if I gave some throttle and then quickly lifted my foot off the accelerator without moving to the next gear. It is not noticeable otherwise.

[paragsachania]

Vid,

Glad that you can now drive smooth without those annoying jerks. If its jerking (unlike knocking), I have also experienced that it is more likely the Ignition System - Plugs, Cables, Ignitors.

At times, while trying to reduce those jerks at the lowest speeds with the AC on, the mechanics have also doubted the Ignitors and were never able to resolve the problem only to realise later that a good set of sparks is what makes these jerks vanish.

In my case, Stock NGK Plugs were never good and I've stuck to Bosch Super since the past 40k Kms and running absolutely fine.

Cleaning with Sand-paper and adjusting gaps might not always reduce the jerks in situations where the electrical system is loaded and the plugs unable to produce seamless sparks to keep the car moving smooth. Even if the plugs are at their End of life state or one or more of the plugs not able to produce that optimal spark should cause this.

Do let us know if the problem is completely resolved

[thelord]

This was an extremely informative thread. I had the same problem in my Alto, though the jerks weren't that bad. So I asked the mechanic to take care of the spark plug cleaning and gaps during the second service and voila! the problem is gone. I think I should be good at least till summers.

[sada]

I have started experiencing the jerks off late with AC on in my BS-III, 2010 Alto which has done 11k on the odo. I am noticing it after the 10k service. The jerks are pretty severe when I remove the foot from the accelerator while coming to a halt and the car is in either 2nd or 3rd gear. This does not happen when the AC is off. Now, my confusion is:
1. Though spark plugs are usually changed at 20k kms, should I go ahead change the spark plugs now itself with Bosch Super as mentioned earlier in this thread? If yes, is there is any particular part # and from where can I buy the genuine one and what would be the approx cost?
2. Can I replace them myself or should I go to MASS?
3. Also, is it necessary to disconnect the battery terminal for some time so that the old ECU setting goes off?
4. Any other suggestion that I could try to rectify this problem.

Regards,

[shady_lawyer]

Does any one know where the blower unit in the 2007 Alto Lxi may be found. I put by head under the dash and was greeted a sticker on the foot blower outlet that reads "sanded vikas cooling unit assy.". I read the wagon-r blower cleaning post however the layout is vastly different!!