Car "hiccuping" on heavy acceleration
10-22-2014, 05:35 PM
#1
AudiWorld Newcomer
Thread Starter
Car "hiccuping" on heavy acceleration
Well, I hope ya'll can help me with this! My car is an automatic. It has nearly 78K miles on it currently with no issues prior to taking the car in for major service at 75K miles. They did a number of things, including replacing the timing belt. When I got the car back I noticed that it felt like I was hitting small bumps in the road on acceleration, but only when trying to accelerate quickly.
When I took the car back to the same mechanic he said it was probably a coil, but after looking into it it was not a coil. He was finally able to reproduce the problem and got a code for an engine power supply relay failure. Once that was replaced the problem persisted. He finally told me that the problem would have to get worse before he could figure out what it is, and didn't want to guess anymore. I appreciate his candor, but I'd still like to know what the heck is wrong with my car! lol
To describe the problem in more detail... I am able to drive it without triggering the hiccuping. As long as I don't "punch it", it won't do it. But if I'm trying to accelerate quickly to get up a hill, quickly get up to speed from stop or slow down it does a series of hiccups (usually 2-3) that feel like bumps in the road. I don't know if it's necessarily power loss because it happens super quickly and then the car runs normally. It did feel like I had more "pep" at initial acceleration after the major service (my car normally has a pretty decent lag at initial acceleration).
Any ideas? Check engine light has not come on.
When I took the car back to the same mechanic he said it was probably a coil, but after looking into it it was not a coil. He was finally able to reproduce the problem and got a code for an engine power supply relay failure. Once that was replaced the problem persisted. He finally told me that the problem would have to get worse before he could figure out what it is, and didn't want to guess anymore. I appreciate his candor, but I'd still like to know what the heck is wrong with my car! lol
To describe the problem in more detail... I am able to drive it without triggering the hiccuping. As long as I don't "punch it", it won't do it. But if I'm trying to accelerate quickly to get up a hill, quickly get up to speed from stop or slow down it does a series of hiccups (usually 2-3) that feel like bumps in the road. I don't know if it's necessarily power loss because it happens super quickly and then the car runs normally. It did feel like I had more "pep" at initial acceleration after the major service (my car normally has a pretty decent lag at initial acceleration).
Any ideas? Check engine light has not come on.
10-22-2014, 09:21 PM
#2
It does sound like an electrical 'miss' so the mechanic started in the same area I would have. If he has replaced the plugs etc in the major service and you said the engine felt like it was running better than before then I assume he has discounted vacuum issues and now electrical issues. So next I would be looking at the fuel mapping. The fact it only does it on power acceleration and otherwise the engine feels like it is running fine, it could just be fuel pressure or the throttle body out of sync when you go to power acceleration.
Do you have access to a Vag-com? I'm thinking during the major service someone may have unplugged the throttle body, perhaps to clean the sensor or something. Anyway, the vag-com program has an adaptation setting to reset the throttle body and the fuel pressure on the A4. Ross-tech site has the procedure. No cost involved so can't hurt trying. The vag-com might also throw up some other codes to hint other issues.
Do you have access to a Vag-com? I'm thinking during the major service someone may have unplugged the throttle body, perhaps to clean the sensor or something. Anyway, the vag-com program has an adaptation setting to reset the throttle body and the fuel pressure on the A4. Ross-tech site has the procedure. No cost involved so can't hurt trying. The vag-com might also throw up some other codes to hint other issues.
10-23-2014, 06:25 AM
#3
AudiWorld Newcomer
Thread Starter
Thanks for the help. I will have my mechanic look into your suggestions! And I have no idea what a Vag-com is. I'll just ask the mechanic. 
10-23-2014, 07:20 PM
#4
Vag-com is a software diagnoses program available to the home mechanic. You can do a search on how to read the error codes before they set off the light on your instrument panel.
There are cheaper options for hand held devices - you plug them into the port under the dash. Options:
1. You can purchase an OBDII reader very cheap that will tell you what most of the more generic engine error codes your ECU has stored. These will tell you a little more than the check engine light but not much. (not recommended - I would be concerned plugging a cheap device into my ECU considering the replacement cost of an ECU, and probably would only find the more obvious problems anyway, but that's my opinion only).
2. You can purchase a dedicated VAG (Volkswagen Audi Group) code reader (eg - Autel VAG505 and others) which will give you all the error codes which helps with the diagnostics, capability to clear the codes, and reset the Electric brakes, maintenance cycles etc. These scan all the systems for the vehicle not just the engine, so you can check the engine, transmission, steering, brakes, door locks, windows etc etc. These are not bad and I used one for a couple of years for general maintenance tasks.
3. The preferred domestic diagnostic tool used by people on sites like this is the Ross-Tech Vag-Com. It lets you see all the errors, reset, do diagnostics and adaptations (recalibration tests). You can print reports and do some pretty detailed diagnoses, including things like real time mapping which may help capture your acceleration issue. This saved me recently by being able to trigger the adaptations on a VW that I was going to be towed. Fixed the problem in the driveway. You do need a laptop to run it on and it's about US$350 so it is a bit of a commitment. If you plan on maintaining the car yourself, it pays for itself in not having to pay mechanics labour. If you can get access to someone else's at no charge, even better. There are pirate versions available on auction sites - look up the cost price for a replacement ECU then decide if you want to risk plugging in a pirate version.
Your mechanic probably uses something else, but they need a system for multiple makes & models.
Post what you or your mechanic finds, there are some pretty helpful people on these sites. Someone can usually identify the problem from a past experience that saves you heaps in time and costs.
There are cheaper options for hand held devices - you plug them into the port under the dash. Options:
1. You can purchase an OBDII reader very cheap that will tell you what most of the more generic engine error codes your ECU has stored. These will tell you a little more than the check engine light but not much. (not recommended - I would be concerned plugging a cheap device into my ECU considering the replacement cost of an ECU, and probably would only find the more obvious problems anyway, but that's my opinion only).
2. You can purchase a dedicated VAG (Volkswagen Audi Group) code reader (eg - Autel VAG505 and others) which will give you all the error codes which helps with the diagnostics, capability to clear the codes, and reset the Electric brakes, maintenance cycles etc. These scan all the systems for the vehicle not just the engine, so you can check the engine, transmission, steering, brakes, door locks, windows etc etc. These are not bad and I used one for a couple of years for general maintenance tasks.
3. The preferred domestic diagnostic tool used by people on sites like this is the Ross-Tech Vag-Com. It lets you see all the errors, reset, do diagnostics and adaptations (recalibration tests). You can print reports and do some pretty detailed diagnoses, including things like real time mapping which may help capture your acceleration issue. This saved me recently by being able to trigger the adaptations on a VW that I was going to be towed. Fixed the problem in the driveway. You do need a laptop to run it on and it's about US$350 so it is a bit of a commitment. If you plan on maintaining the car yourself, it pays for itself in not having to pay mechanics labour. If you can get access to someone else's at no charge, even better. There are pirate versions available on auction sites - look up the cost price for a replacement ECU then decide if you want to risk plugging in a pirate version.
Your mechanic probably uses something else, but they need a system for multiple makes & models.
Post what you or your mechanic finds, there are some pretty helpful people on these sites. Someone can usually identify the problem from a past experience that saves you heaps in time and costs.
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11-28-2016, 11:27 AM
#9
I have a 2009 A4 that exhibited the exact same problem, almost like a cough during hard acceleration under load.
Took it to the dealer, and he said that 3 of my 4 ignition coils were on their last legs and that I should replace them asap or I could be left stranded.
That's scheduled in 2 weeks and will report back on results.
Took it to the dealer, and he said that 3 of my 4 ignition coils were on their last legs and that I should replace them asap or I could be left stranded.
That's scheduled in 2 weeks and will report back on results.
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Rochelle13 (10-18-2021)
11-30-2016, 01:13 PM
#10
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Had symptoms like what you describe in our A4 and the carbon clean (walnut blasting) fixed it in our case. I noticed it most when pulling up a steep hill near our house - if I gave it some throttle it would feel like it was hesitating, and the power wasn't quite there.