Slight hesitation upon initial acceleration 2003 V70 Topic is solved

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unggthat
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Year and Model: 1999 V70T5, 2003 V70
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Slight hesitation upon initial acceleration 2003 V70

Post by unggthat »

I have a new-to-me 2003 NA V70 automatic with 186k. It was a bit rough at idle but otherwise drove nicely. My usual deal is to go through and do all the basic maintenance on these cars and then drive them a long time, so I started in. First, cleaned the throttle body and changed plugs and coil packs. Idle improved some (went from around 700 to a nice 850-900RPM) but I can still feel a little rumble at idle. I changed all the fluids (transmission, oil, brake, antifreeze) this weekend, and did the timing belt, as it was time.

Now the idle is even more improved though not quite perfect. After this weekend though, there is a little hesitation upon initial acceleration. It feels like if I push the pedal 30% of the way, it starts off as though I've pushed it 10% for about two seconds then it goes back to normal. If I gun it, it goes just fine. There are no error codes stored in the computer (there was a MAP sensor code before but the throttle cleaning fixed that). No check engine light. It generally feels like it's running fine except for this weird slight hesitation.

Any guesses what I should look at? If the timing belt was off a tooth, it would not run well (been there before). Could it be an issue with the throttle module? Thanks for any help!

Nate

ignatz
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Post by ignatz »

If you checked the compression, and that was ok, I'd add two bottles of Chevron Techron and get it thru the system. I've had injectors clear themselves out by adding this stuff. Also, it can take days for this stuff to work. And I added this stuff to my 93 Mercedes to clear the injectors. Its something to do to see if it gets better.
98 S70 T-5

unggthat
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Post by unggthat »

Thanks for the idea--ran a bottle through and it didn't make a difference. In fact, it's getting worse, especially when the engine is cold--if left outside it often stalls after first startup. Compression test looks good. Fuel pressure sits around 3.75-3.8 bar--supposed to be 3.8, right?

I've already ordered some rebuilt injectors and a fuel pressure sensor. Any other good way to check the fuel pump? Could it be the PEM?

I have no codes showing up, but this certainly seems fuel related. Thanks for any ideas!

Nate

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Post by csh »

unggthat wrote: Mon Jan 04, 2021 8:57 pm First, cleaned the throttle body and changed plugs and coil packs. Idle improved some (went from around 700 to a nice 850-900RPM) but I can still feel a little rumble at idle.
That does not sound correct. That idle speed is too high
unggthat wrote: Mon Jan 04, 2021 8:57 pm I changed all the fluids (transmission, oil, brake, antifreeze) this weekend, and did the timing belt, as it was time.

Now the idle is even more improved though not quite perfect.
Placebo effect? I can't see any of those items having a meaningful improvement on idle. The one exception is the oil change if the oil level was low before the change.
unggthat wrote: Mon Jan 04, 2021 8:57 pm After this weekend though, there is a little hesitation upon initial acceleration. It feels like if I push the pedal 30% of the way, it starts off as though I've pushed it 10% for about two seconds then it goes back to normal.
The high idle plus this is makes me think that the throttle body needs recalibration. I had a similar problem after cleaning the TB on my 2004. I turned the key to the on/II position without starting the engine and left it there for 60secs or so. That seemed to have allowed the TB to recalibrate and solved the problem for me. This may work on you 2003 as well so it might be worth a try.

To be honest this 5 cylinder does not have the smoothest idle and bad engine mounts will make it more noticeable. I would inspect the upper and lower torque mounts and probably just replace the mount by the crank pulley. I replaced the mount by the pulley when I did my timing belt and it made a noticeable improvement even though I still had a poly for the top torque mount. Once I decided to go back to OEM for the top torque mount that made things feel almost as smooth as when the car was new. If the engine runs smooth above 1k RPM I would suspect your problem with the rumble is the mounts. Note that there are two more mounts to front and rear of the engine. I'm not sure how often they fail, but given the mileage and age of your car, that is possibility.

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oragex
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Post by oragex »

In theory the throttle body for the NA is quite simple inside but there is a plastic gear that may still get some play to it. Hard to say without opening it, and opening it is risky, however any used one is plug and play. Usually when the key turns in POSII without starting, the tb will buzz for a while to adjust.
I'd start with the basic, a quick look at the timing belt by lifting the upper cover - detach the metal clip, lift a little toss the left cover a little and look with a flash light at the belt. When I buy a car I like to make sure the parts used for the belt replacement were quality ones, as cheap ones don't last and start to seize. Next would be a PCV test (youtube). You may also have a vacuum leak somewhere - multiple possibilities, including throttle body and intake manifold gaskets

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Post by kallekula »

Have you checked fuel trims?

BMW 540i 2002
S70 Base 2000

unggthat
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Post by unggthat »

csh wrote: Sat Jan 16, 2021 8:33 am That does not sound correct. That idle speed is too high.
My Haynes manual says that idle speed should be 850. That's right where it is...Am I missing something? You seem to think that's too high?
kallekula wrote: Sat Jan 16, 2021 3:20 pm Have you checked fuel trims?
How would I check the trims? I put a gauge on the shraeder valve and it ran pretty even at 3.8 bar. My OBD scanner readout told me the same, though it sometimes dropped a bit down to 3.65 for just a split second as I pushed the throttle, immediately coming back up to around 3.8 bar.
oragex wrote: Sat Jan 16, 2021 1:31 pm I'd start with the basic, a quick look at the timing belt by lifting the upper cover - detach the metal clip, lift a little toss the left cover a little and look with a flash light at the belt. When I buy a car I like to make sure the parts used for the belt replacement were quality ones, as cheap ones don't last and start to seize. Next would be a PCV test (youtube). You may also have a vacuum leak somewhere - multiple possibilities, including throttle body and intake manifold gaskets
I replaced the timing belt already. Definitely not off a tooth. This problem was present before and after the belt replacement. Would there be something with resetting the variable cam gear that could affect this? Basic hand-on-oil-fill-spot passes PCV test, though I have all the parts to redo the system. Next weekend I plan to do the PCV system, injectors, and double check for any vacuum issues. As an anecdotal aside, my '99 V70 T5 had a 10" section of vacuum hose totally collapsed and broken this week and was still running really well--driving it felt totally normal.

General update: I replaced the fuel pressure sensor. Changed out the throttle body to one from my other V70 of the same year and recalibrated. Same issues persist: slow to get going from a stop. When car is left outside in the cold (it's winter here in Ohio), it sometimes stalls when first turned on. It does feel generally a bit under-powered compared to my other V70 non-turbo of the same year...

I am waiting on fuel injectors to arrive then might check the PEM.

Thanks again!

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kallekula
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Post by kallekula »

unggthat wrote: Sun Jan 17, 2021 6:32 pm
csh wrote: Sat Jan 16, 2021 8:33 am That does not sound correct. That idle speed is too high.
My Haynes manual says that idle speed should be 850. That's right where it is...Am I missing something? You seem to think that's too high?
kallekula wrote: Sat Jan 16, 2021 3:20 pm Have you checked fuel trims?
How would I check the trims? I put a gauge on the shraeder valve and it ran pretty even at 3.8 bar. My OBD scanner readout told me the same, though it sometimes dropped a bit down to 3.65 for just a split second as I pushed the throttle, immediately coming back up to around 3.8 bar.
oragex wrote: Sat Jan 16, 2021 1:31 pm I'd start with the basic, a quick look at the timing belt by lifting the upper cover - detach the metal clip, lift a little toss the left cover a little and look with a flash light at the belt. When I buy a car I like to make sure the parts used for the belt replacement were quality ones, as cheap ones don't last and start to seize. Next would be a PCV test (youtube). You may also have a vacuum leak somewhere - multiple possibilities, including throttle body and intake manifold gaskets
I replaced the timing belt already. Definitely not off a tooth. This problem was present before and after the belt replacement. Would there be something with resetting the variable cam gear that could affect this? Basic hand-on-oil-fill-spot passes PCV test, though I have all the parts to redo the system. Next weekend I plan to do the PCV system, injectors, and double check for any vacuum issues. As an anecdotal aside, my '99 V70 T5 had a 10" section of vacuum hose totally collapsed and broken this week and was still running really well--driving it felt totally normal.

General update: I replaced the fuel pressure sensor. Changed out the throttle body to one from my other V70 of the same year and recalibrated. Same issues persist: slow to get going from a stop. When car is left outside in the cold (it's winter here in Ohio), it sometimes stalls when first turned on. It does feel generally a bit under-powered compared to my other V70 non-turbo of the same year...

I am waiting on fuel injectors to arrive then might check the PEM.

Thanks again!
I should have written: Have you checked for vacuum leaks?

BMW 540i 2002
S70 Base 2000

unggthat
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Year and Model: 1999 V70T5, 2003 V70
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Post by unggthat »

Update:

Today I changed the injectors to reman ones, redid the breather system, and replaced some vacuum line. Took it for a test drive. Possibly better? But still not perfect.

Symptoms: the car just doesn't have that much power compared to my other identical one (both NA '03 V70s). This one has 100k fewer miles on it, so I figure it should be the spunky one (186k vs 276k)! It gets 1-2mpg less than the other one. Sometimes if it's sitting in the cold it will start but then dies when you go to move. Then it restarts and keeps going. From a stop, the engine hesitates to really pick up for a few seconds then kicks in pretty well. It doesn't idle as smooth as the 4 other white block cars I've owned over the years, including the two others I have right now. It sits at 850rpm but has a small rumble to it. Compression is good.

What I've done:
1) All vacuum lines checked/renewed
2) Air filter
3) Plugs and coil packs
4) Timing belt, water pump, idler and tensioner pullies
5) Engine breather system replaced
6) Fuel injectors and pressure sensor

Curious discovery: The fuel system is running at 3.8 bar. But in my Haynes manual, it says the Denso fuel management system should be at 3.0 bar. I'd check it on my other '03 but it's currently getting a new transmission. Can anyone confirm I should be running 3.8 bar? As this is electronically controlled, I'm not sure how I'd change it anyways....but there it is.

I'm heading down the road of just throwing parts at it now, I recognize. I don't get any codes. If I didn't have so many other Volvos to compare it to, I'd probably not think much of it. However, I want this car to be our main car for trips and want it running really well. I may end up taking it in to an indy Volvo guy...haven't taken in a car in over 10 years except for alignments!

If anyone has guesses or ideas of what to check, let me know. Thanks again!

unggthat
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Post by unggthat »

Final update before I'm taking it to a shop:

Replaced the PEM with a used one today: no change

Discovered my reader (iCarsoft Volvo OBD tool) can do fuel trims: short-term and long-term fuel trim all sits around 1 (between .96 and 1.01). The cylinder specific fuel trims all said the same thing. I assume that's pretty good? Fuel trim is not something I'm well versed in.

I'm partly writing these steps I've taken here so that some other poor sap with similar experience can follow it! I'll post after I take it in with what it was.

If anyone has final guesses as to what I might look at, I'm all ears!

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