Idling issues, checked MAF etc

Raycharles90 · Post by **Raycharles90** » 04 Oct 2012, 11:31

Hi,

This is my first post and I hope that I am clear and concise. I have a 98 s70 with 138,000 miles. I purchased it from my sister in 2008 so prior to that much of the history is unknow. For the last 3 years I have had idling/vacuum issues on an off again. In the past I have replaced the vacuum lines. I did the ones that I could easily access. I did not replaced the pcv valve or associated lines that run under the gasket. At that time I put a remanufactured MAS on and all was good. During all of this the only code that it threw was P0455.

In the last few weeks the idling has again started to act up. While sitting at a light it would drop down to 600 rpm. I would get home by just slipping in to neutral and maintaining 1100 rpm then putting it into gear. Unplugged the MAS and it worked well for a day then started acting up again.

Brought it in and had the throttle body cleaned and the mechanic recomended a new MAS. Just put the new (Bosch) in and the problem is still the same althought less so. It will start fine and idle around 1100 then drop down to 900. After a minute or two it will drop down to 600-700 for a couple of seconds then pop up to 1400 for a bit then back down to 900. After a bit it will fall all the way down to 300-400 for about 10 seconds (feels like eternaty) then pops back up to 900-1000. After this it doesn't trip the light or throw a code that i can see.

I tested the Fuel pump relay switch and that seems fine. Could it be the throttle position sensor? I am fairly able to do this myself. The mechanic that I have is ok but he was talking to me about motor mounts which is about as helpful and commenting on the cracked leather.

Would love any of your comments, Thanks

Post by **kcodyjr** » 04 Oct 2012, 11:47

Actually, mine was doing this, and mysteriously stopped when I had the totally collapsed right front engine mount replaced. No idea why; maybe it was just pinching or bending a hose because it was leaning over so far.

By the way, you do know that Ray Charles was blind and presumably didn't drive Volvos or anything else?

Post by **erikv11** » 04 Oct 2012, 11:54

Did you try cleaning the Idle Air Control (IAC) valve? If the problem is only at idle, that might be a better place to start than the TPS. Plus, you can clean the IAC but not the TPS, so worth a try.

To clean the IAC you must first remove it. Pretty easy on an NA. Those one-time hose clamps (if they are original) you can just replace with regular worm drive clamps. Remove IAC, spray a good dose of carb cleaner in there, shake it around real well (be careful not to splash it onto your face etc), then dump it out. The valve should move freely when you rotate the IAC. If it rotates fine when you take it off then the IAC may not be the problem, but it is a good idea to clean it anyway.

Did you check the vacuum elbow hiding below the PS pump, on the end of the intake manifold? It is notorious for cracking and creating a vacuum leak.

Raycharles90 · Post by **Raycharles90** » 04 Oct 2012, 13:22

Thanks for your ideas. I will clean the IAC tonight. I will also check that elbow. I thought I was pretty good at looking at everyone but I could have easily missed that one. The strange thing is that it will not stall out. It just shakes and rattles at 300-400 rpm for a bit then pops back up to normal idle.

I am quite sure my right front mount needs replacing. Before my sister had the car it was my Aunt's. She had it for the first 60,000 and did everything at the dealer. When my sister got it that is when regular maintenance stopped. I have been working through a lot of these when I get a chance. Put new plugs in a couple of years ago, new upper motor mount, replaced most of the fluids, need to do the drain and top off for the tranny. But this vacuum line fuel issue gremlins have been goating me for a while.

I should say that in 2008 while evacuating from a storm I found a nice gas station with a special on watered down gas. Made it to my destination but shortly after blew the MAS. Replaced that and did a series of gas treatments and put two new fuel filters before that all got out of the system.

Thanks again and if anyone else has any suggestions I am all ears. Also, Ray Charles is a family name but also a darn fine musician.

Raycharles90 · Post by **Raycharles90** » 05 Oct 2012, 11:24

So I pulled off the IAC last night and it was pretty gunky. I also noticed that there were no clamps on the hose going to the vac tree and down to the tube leading to the MAF and air filter. So after cleaning it real well with carb cleaner I noticed a big improvement. I reset the computer and then started it up. I let it idle for 5 minutes. It started around 1100 then dropped down to 900 and remained steady. I then popped it into drive and went around the block. So far so good until I got to the last stop sign. I could see the needle drop down to ~700. Put it into neutral and revved it up a bit then went around the corner and parked the car and let it idle. It stumbled around 600-700 rpm for a couple of seconds then jumped up to 1500 then dropped down to 900 and remained steady. After about 5-7 minutes I could feel it start to stumble again, I tapped the gas and it steadied out again around 900.

At this point I am thinking it is a small vacuum leak. Erikv11, you mentioned the elbow below the PS pump. I visually inspected this but would I need to remove the large water hose to access this? I have some extra silicon tubing from my vacuum line kit and will just remove the elbow if easily accessible.

I know that I need to do the pcv valve as my car has failed the dipstick test from the time I purchased it. I just have been avoided doing this. Could this be a culprit?

Bottom line; much better now than before but, still not great.

Thanks again, This volvo has been a learning experience from the get go but I don't mind tinkering.

Post by **regent** » 05 Oct 2012, 15:09

Blocked PCV system is definitely a good reason for erratic idle. You are on the right track!

rick4484 · Post by **rick4484** » 05 Oct 2012, 17:21

I'm having the same issues with my 98 S70 T5. Just bought a new MAF because when I disconnect the old MAF connector it idled ok. The new MAF from DW is OEM and the car runs a little better but still the idling problems continue. I just did the PCV service, new plugs, new plug wires, changed some vac lines and elbows too. I'm starting to suspect a vacuum leak.

My problem started about a week after the PCV service. While cruising on the freeway I noticed a sudden reduction in power and pulled off the freeway. Had to keep my foot on the gas pedal and the brake to nurse it home.

rick4484 · Post by **rick4484** » 05 Oct 2012, 18:26

I just fixed my problem. I found that I didn't tighten the big hose clamp on the throttle body. I was taking off the IAC to clean it and the big hose popped loose from the TB. I guess when I did the PCV service I forgot to tightened this clamp. Well that cost me about a $180.00 for a new MAF, which I probably didn't need. I cleaned the IAC anyway, tightened all the hoses and now she runs great. So, recheck all you hose clamps!

Post by **erikv11** » 05 Oct 2012, 20:54

Hope you saved your old MAF?

Raycharles90, that elbow is part of the PCV job, for the record.

You can remove the elbow with loonnnnnnng nose pliers, I have a pair that is like 8 inches and have used them before for that purpose. No need to remove the upper radiator hose, just get a good light and some long pliers. Replacing it with silicone or some other (new!) hose is a good idea to rule it out. The other end connects to the nipple on the flame trap housing, although TBH I am still wondering if it wouldn't be fine just to cap off the nipple on the manifold. Never tried that.

You don't have to route the replacement under the intake manifold, just get it connected over the the correct spot.

Raycharles90 · Post by **Raycharles90** » 07 Oct 2012, 11:24

Well just found the issue. May post a picture if I can take a good one. So that vacuum line runs under the manifold and connects to the PCV (correct?). So upon further inspection of the PCV I noticed that it wasn't seated very well and that little vac line was broke of at the pcv. So it looks like I will be doing the PCV job here. I may run vac line to see if it will work until the new valve comes in.

Not sure how I missed it before. But thanks, will report back.