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Surge only at idle speeds

2K views 8 replies 3 participants last post by  PatrickPeru 
#1 ·
I have a 2008 Hyundai Santa Fe. Has about 65k miles on it and has regular maintenance and tune ups when needed. It is cared for. The last tune up was about 2k miles ago. Spark plug change, oil change, filters, etc.

I have noticed lately that when the car is moving at idle speeds, it will surge about 200 rpms. It does not happen when the breaks are on or stopped or in park, or moving at higher speeds. It only does it while moving and with no acceleration. It happens in Drive and Reverse.

I live in the city of Lima Peru so a 4x4 is useful but it also requires some tight parking but when it starts to surge, it is a huge pain. My mechanic is good but I have to be able to give him an idea of what to look for so getting specific ideas is helpful. My Spanish is growing but car stuff is still new to me.

Any help is appreciated.
 
#2 ·
When you first fire it up in the morning, does the engine also wander a bit looking for an idle speed? I'm not talking about the normal high rev that drops down to something normal, I'm talking about after it drops down .. does it settle or wander? If it wanders around looking for a solid idle speed, go directly to Throttle Position Sensor replacement.

Have you had the scan done for codes?

The reason I ask is that your symptom sounds similar to those presented by a bad throttle position sensor, something common on an '08 engine here. Cheap to replace with the newer version.
 
#3 ·
Nope. It finds its idle perfectly and idles perfectly. Never have an issue with it idling at stop lights or after heavy use. I have not asked for it to be scanned specifically, but the shop owner, who I trust for a third world mechanic, said he saw no codes.


It does make a ticking noise from the throttle body area that they said is normal. It ticks slowly for about 35-45 sec and stops for about 5-10 then starts up. It get quicker with acceleration until its almost one continuous noise.

Thank you for the reply and hope this info helps.
 
#4 ·
The thing that the TPS is sensing is the ETC motor that is the other end of the fly-by-wire system that starts at the pedal. That's about all there is in the area of the throttle body that moves, but honestly, I've never heard one doing any 'ticking'. It's a simple +/- DC dual gear drive, not normally pulsed in any way. I'd be curious to know what your shop believes is a component in that area that should be 'ticking'. I'd guess it's coming from somewhere else.

Be that as it may, since you're not experiencing problems at idle, and you have not yet seen any codes, there's no special reason for pointing at the TPS except for the fact that it so often causes this symptom, but usually among others. However, there have been a fair number of reports of symptoms showing up even prior to the typical set of codes (P161B, P1295 and P2106) popping up. Won't surprise me if you eventually see these. If you do, you'll also get the MIL on the dash telling you to check for codes. TPS is pretty common failure item on this vehicle. I assume you the original owner and hence know the full service history?

While engine surging can come from many places, this is the only weak spot in the '08 design that has been reported to have caused it that I can recall. All of the other possible sources for 'surging' should also be popping codes, and don't fit your specific symptom. Partially plugged fuel filters and failing pumps, vacuum leaks etc won't usually just show up at idle speeds nor only when the vehicle is in gear, they'll bother you across a range of RPM. Surging at idle, especially by so few RPM, is much more an indication that the 'computer' is overcompensating for something it's seeing from one of the sensors.
 
#6 ·
I was actually thinking the breaks. Either they were seizing or a vacuum. Come to think of it, as I now need to test this, once I have moved forward quite a bit in idle speeds, it stops surging.


Got any info on checking the hoses out or is it better to let the mechanic do it?
 
#8 ·
It is possible you will be placed in 'limp home' mode with limited RPM if it does go completely south, but the vehicle should be driveable.

As for vacuum leaks mentioned above, any vacuum leak that causes driveability problems will pop a code almost immediately due to inability to keep fuel trim correct. Common ones are cracks of the rubber boot (always check carefully underneath the boot) that connects the throttle body. But you have no code for that, either.

You may have to wait until the problem becomes bad enough to finally get you something you can scan.
 
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