98 S70T5 The Never Ending Saga of Idle issues.

Scholz · Post by **Scholz** » 10 Sep 2015, 22:26

I'd like to preface this post with a giant thank you to everyone who has helped me thus far.

When I traded a laptop for this volvo ( never owned one nor thought to) My original plan was to harvest it for parts and junk the rest in my spare time. It ran terribly and the PO had received it in a trade himself and had no idea or desire to try to fix it. I have no clue of the service history other than the engine compartment is near spotless and the timing belt was done 55k miles/6 years ago.

It ran far too lean with associated CEL. A quick bit of research and i determined the pcv system was shot. (It was, so i serviced that along with plugs, wires, cap/rotor and a change of oil.)

The two hour drive I took with it after I finished that changed my entire outlook on the vehicle. I went from looking to junk it, to wanting to preserve it for all of eternity. This is a seriously fun car to drive, handling and everything. I enjoy it more than my 04 Subaru WRX, my tuned out ricer (90' civic with a d16 block and jdm vtec head) or the 98 mustang.

The car boosts and pulls great, vacuum is steady around 24HG at idle and boost gets up to 10.5psi or so according to the gauge. MPG is right where it should be based on car specifications.

That being said, my idle has never been right. It used to be far worse, trying to stall sometimes, hard starts etc. So i've completely redone almost every vacuum line in the car aside from the brake booster. New MAF solved most of the issues and she never tries to stall anymore. New TPS has been thrown in to no effect, IACV/TB cleaning done. (Was truly truly filthy.)

What I'm left with is when coming to a COMPLETE stop the rpms dip down to ~500 or so and quickly come up very similar to the issues I've read about with failing ETM's but I don't have one. The IACV is clean as clean can be and i can hear it rotating and slapping the ends of itself when i twist it. The issue is slightly exasperated with the A/C on, but happens without. Hot/Cold isn't an issue. ETC readings are normal (Fan comes on around 103 Celsius).

In the past 5 months I've done the following.
PCV overhaul - OEM
MAF - Bosch
OEM Plugs
Bosch Cap/Rotor
Wires - NAPA brand. (No issues at all with misfires, might swap to Bougicord anyway)
New Blue box Fuel Pump/Relay
Air Filter (Local auto parts store store brand, NAPA maybe)
New IPD HD TCV (My Pierburg unit snapped in half trying to replumb the vacuum lines.

)
New Front Oxygen Sensor - Bosch
Throttle Position Sensor - Bosch
Oil change 3k miles ago using 10w30 full synth

I'm at a loss at this point. I don't suspect transmission issues, shifts are smooth, kickdowns during hard accelerations are on point, and while being horribly colorblind so I can't see how red it is, the transmission fluid is at the correct level and not burnt.

Sorry for the long winded post. any thoughts are appreciated. I'm collecting the parts for a complete cooling system overhaul next weekend (small weeping of coolant from radiator side tank on the engine oil cooler side.) that will include a new temp sensor.
At this point i'm looking to perhaps try a junkyard IACV, or maybe have a look at the ignition coil? I don't know.

Post by **abscate** » 11 Sep 2015, 01:49

Try coasting to a stop without foot brake to see if you can diagnose a vacuum leak theory. This assumes your e-brake is in good condition and not locked up

Scholz · Post by **Scholz** » 11 Sep 2015, 02:24

What am i simulating? letting it coast to a stop in neutral? or using the e-brake to do the stopping in gear?

Post by **kahl** » 11 Sep 2015, 09:28

I think he is wanting you to see if your brake booster drum is leaking. So coming to a stop keep your foot off the brake pedal, use the parking brake to come to a stop then see if you get a RPM drop.

Scholz · Post by **Scholz** » 11 Sep 2015, 13:02

The RPM dip wasn't nearly as pronounced today as it had been previously. It didn't go below 800 until i turned the AC on. That being said using the ebrake to stop didn't change the behavior all that much. Brake Booster holds its vacuum as it should (testing with car off and starting with pedal depressed after bleeding the vacuum off.)

I 've read over and over that i should be using Bougicord/OEM plug wires, but I've not seen any documentation as to what the vehicle has issue without those installed. Electromagnetic radiation leakeage maybe? The only reason I ask is maybe 25% of the time under WOT my significant other and I's phones will lose our bluetooth connection, Perhaps thats an ignition coil thing. I don't know.

Post by **abscate** » 11 Sep 2015, 23:37

It might be worth taking off the serpentine belt and seeing how much resistance is in the AC clutch and compressor. If it's seizing that might be the culprit?

Scholz · Post by **Scholz** » 12 Sep 2015, 22:34

So, I think for now I may call this solved? After the Idle Air cleaning three days ago, and a complete transmission fluid flush I embarked on quite a bit of driving today and noticed the dip steadily getting better in severity. At this point even after redlining in 3rd gear and coming to a stop as quickly as I could safely I can barely cause the dip now.

Perhaps it took the ECU/TCU some time to relearn after the cleaning and fluid change but I think i finally have a stage zero setup going. To say I am ecstatic is an understatement. 277k and with the engine and tranny feeling better than vehicles 10 years newer, feels like she could go another 277k.

Scholz · Post by **Scholz** » 26 Sep 2015, 16:10

So, The problem ended up coming back shortly thereafter and began getting worse and worse. I cleaned and inspected the IACV again and found nothing wrong. I ended up buying a new to me IACV off a poor guy parting out his v70t5.

Cleaned that one up and compared the two. Both baffles rested in the same location, and moved the same way when i rotated the unit. However, the new unit solved the issue immediately and it has not sprung back up since in the two weeks i've had it in.

So after all of that it ended up being the IACV, I guess the electronic portion of it had gotten tired. Which is odd as it idled fine after the rpm drop aside from a once a week stumble for a second or two. I don't know how the motor actually operates so I can't fathom the failure in the unit to be honest.

Post by **mecheng** » 26 Sep 2015, 16:48

Interesting, I have the same problem but it only happens once in a blue moon. Say once every 4 months. Tune up,doesn't help. Because it's so rare I just ignore it. I also have a 98 t5