1998 S70... non-running [MAF/engine electronics issue?]

BeachWagon · Post by **BeachWagon** » 26 Jun 2017, 12:14

Recently, I became the proud owner of a 1998 Volvo S70 Turbo, just shy of 160k. More than a fair trade for fixing a cellphone. The guy was up front with me...it needs some help.

THE BAD: Front suspension is pretty far shot. Interior needs some love. Oil leak somewhere around the turbo. Engine management electronics are having a hissy fit. Trunk lid is dented pretty bad but still opens and closes. Both passenger side windows don't go down. Power seat has no power. Heater core is leaking. Other benign old car issues...

THE GOOD: Dude just replaced the wastegate and MAF sensor. He also included a new heater core with the car, but never installed it because he got tired of its issues with wanting to run correctly[we will get to that soon]. Engine is very quiet and runs very well when it wants to, and the transmission shifts perfectly. Brake system is strong. Sunroof works. AC works[cycles compressor kinda frequently, probably low on refrigerant.] TOTALLY rust free.

So the night I acquired it, it started, idled like crap and shut off after a moment. Some skillful throttle feathering and gear shift work got it started and well on its way home. Then it warmed up. As the engine temperature climbed, it got worse and worse until I was sitting in a parking lot with it moving no more than a foot before shutting off again. It got bumper-pushed home by my faithful old Buick. After exploring the engine bay, I determined that both charge pipes were disconnected from the intercooler. Weird. It wanted to run marginally better after that issue was alleviated, but still a lot of angry shaking, sputtering and idle hunting. Throttle was needed to keep the engine running. Google search told me to unplug the MAF. Runs perfectly aside from a little bit of idle hunting, and hesitation when i put my foot down. Otherwise it will run fine. Switching from the new MAF provided with the car, to a junkyard pull from a perfectly running and driving car, yields the same results. MAF plugged in, total chaos. MAF unplugged, idle is a little weird but very driveable. Also getting P0102 and P0171 when MAF is plugged in??

So here I ask, what could be causing this?

Post by **FLXC90** » 26 Jun 2017, 14:52

Lots of vacuum lines for you to check. (skillful feathering...) also lean condition, look for unmetered air infiltration, something direct to the manifold, downstream of the MAF. (Vacuum tree-brake booster-PCV) Also your turbo and intercooler air hoses. Happy hunting

BeachWagon · Post by **BeachWagon** » 26 Jun 2017, 16:13

SO Im guessing even the slightest leak would send it into a fit? As I read more about this system, I assume its quite sensitive. This car seems to have a fairly intricate vacuum system.

BeachWagon · Post by **BeachWagon** » 27 Jun 2017, 14:28

Quick update. Drove it cold to the local convenience store this morning, MAF unplugged. It gave me a lot of trouble until the engine warmed up. Also learned that it has turbo flutter, so CBV may be bad. I have the day off tomorrow so I'll be investigating that as well as vacuum lines. Perhaps the CBV vacuum line is disconnected/trashed, causing both issues? I'll know for sure tomorrow!

BeachWagon · Post by **BeachWagon** » 29 Jun 2017, 16:45

Last day was spent carefully removing all the airbox/intake hose bits from the engine bay and making notes of where they go. Gonna run all new vac lines because a lot of them are deteriorating, and a couple crumbled away/broke from me simply removing them from their connectors. My hands were covered in black dry rotted rubber. My plan is to replace all vac lines as well as service the PCV system while I am this deep into the engine. I did find some oil puddling on top of the engine as well as smoke coming from the dipstick tube. She needs some help but I'm ready!

http://volvospeed.com/vs_forum/uploads/ ... 163714.jpg

Does this look like the correct vacuum diagram for my car? If so, how would I go about testing the solenoid valve, purge valve and check valves?

Anything else I should knock out while I'm messing with all of this? Any common failure parts I should just go ahead and replace as preventative measure?

Post by **scot850** » 29 Jun 2017, 19:42

Not sure if this is the vacuum diagram for your car, but obviously is a turbo engine. Some cars have the diagram stuck under the hood, so may be worth checking there.

The TCV is a common failure point with age. It will prevent boosting or make it random how much boost you get. I'd do as you suggest and replace the vacuum lines first before checking the components for issues. PCV pressurising does not help the equation as it can cause issues with engine vacuum.

The pool of oil could be one of the 2 rear cam seals leaking by the distributor.

Once you have replaced the vacuum tube, you can test the CBV by pulling a small vacuum on the hose to the TCV and see if it holds it or not. With the turbo you have you should be able to access the 3 bolts to replace the CBC diaphragm without removing the turbo.

Good luck!

Neil.

Post by **abscate** » 30 Jun 2017, 00:02

A turbo will run horribly with connected MAF and air leaks. Replacing everything is a good first step, then move to ignition and looking at plugs , cap, rotor, wires

The hose on the Idle air control valve likes to split

BeachWagon · Post by **BeachWagon** » 01 Jul 2017, 10:20

Scot850: forgive my ignorance, but what is the TCV?

abscate: Agreed! The MAF being connected was horrible. The ignition system appears to be in good shape, as if it had been somewhat recently replaced. I removed the cap and wires, since they were in the way.

Is there anyone that knows how to test those check valves and solenoids??

Post by **scot850** » 01 Jul 2017, 18:02

No apology needed. TCV is the Turbo Control Valve. It has 3 tubes going to it and usually mounts on or near the airbox close to the distributor in a 98. It controls the amount of boost to the turbo, and the pipes to it disintegrate. One of the pipes runs to the CBV and that is the one to pull from the TCV to test if it can hold a vacuum.

If the car ran poorly when cold and better when warm, it may be pointing to the engine water temp sensor under the thermostat (ECT). There is a method to check the resistance on the ECT when installed at various temperatures. The connector is usually mounted on the body of the power steering pump. The connector and wires to is are also a known weak spot as the cars age. Test the ECT and clean the connector with contact cleaner, let dry while checking the wires for condition.

Neil.

rocketman4321 · Post by **rocketman4321** » 01 Jul 2017, 21:13

+1 on the cam seals, especially if there's oil on the turbo or on top of the transaxle. It's impressive how much they can leak. I've also had the intake one leak into the distributor and cause stalling and misfires. Avoid Elring replacements. If the oil is "on top" around the oil filler and spark plugs, it's likely the oil filler cap gasket or the PCV hose that goes up there came off.

Once you get the vacuum lines sorted out, if the MAF is still funny there's a test. Recommend searching for it, but from memory pins 1 and 2 of the MAF connector are grounds, pin 3 should be ~+12V when "on", and pin 4 is the signal input. Test for continuity to ground and voltage on pin 3. Then with it connected peel back the rubber cover of the connector and put a small nail or pin into pin 4 until you have contact. The voltage there should be a couple volts at idle (sorry, mine wasn't close so I forget the value) and should change with engine speed. With the car off you can also check the input impedance to the computer--pin 4 to ground should be about 19 kohms. Again, please check all these values as I did this a couple weeks ago. But this will confirm the wiring is OK and the MAF is at least somewhat working (mine wasn't).

If the car's been unloved, +1 on cleaning connector contacts as you go. That said, I've rarely seen a dirty one fail.

As part of your go-through, I'd pull the IAC and clean it with carb cleaner. They get gunked up and stick. The valve should flop freely when you roll it over.

The ECT (coolant temp) sensor is easy to unplug and test. Mine measured about 2000 ohms when it was ~ 75F, but the car had been parked in the sun on a hot day for the afternoon. I think the spec is 2900 ohms at 20C (68F) and it goes down with temperature. But I agree that this comes after vacuum, IAC hoses and operation.

Good luck! These are great cars, they do take a little work, but they also respond well to that work. If you don't mind the work, keep plugging and you'll have a solid car.