1998 V70: CEL with no code; bogging down at idle

S Carlson · Post by **S Carlson** » 22 Jun 2021, 12:54

Here's a problem that's got me stumped.

'98 V70 T5 automatic (normal cable-controlled throttle, no ETM) gets a check engine light occasionally. Mostly in city driving, mostly after filling the tank or on a very empty tank. When I go to pull the codes, there's no code!

It also bogs down at idle, and if it does this, I may have no power accelerating. Usually turning the car off and back on again fixes the problem for the time being. Turning on the A/C seems like it may even things out, but sometimes it has no effect.

One time, I did get a code: P0455, major evap leak. I cleared it and it never came back.

I just did the PCV system, distributor cap and rotor, spark plugs, and wires. It had the same problem before and after, as if I'd done nothing at all.

So, what's the course of action? I can visually inspect the evap lines for disconnected or rotten bits, for sure, maybe test the purge valve. Other than that, I'm stumped even after hours of searching.

Differential diagnosis could be the fuel pump or fuel pump relay, both of which seem like they'd make the engine stop completely or fail to start, so I suspect them less. Perhaps check the charging voltage to make sure I'm not somehow getting a short on the alternator causing it to put a ton of load on the engine. Seems like the idle air control valve would not cause the car to bog under acceleration too - like I'd be able to rev out of it.

Does this problem sound familiar to anyone?

Post by **scot850** » 22 Jun 2021, 14:15

Check your water temp sensor is working. It is a classic issue and will over-rich the fuel if not working correctly.

Check fuel pressure when engine is warm. Could be the pump is dying but is ok when cold and seizing as it heats up.

A major air leak would cause an issue especially with a turbo. Check all vacuum lines and the pipes from the air box to the turbo including for cracks in the intercooler.

Major air leak could be the evap system pipes have a crack in them at some point. Not sure on your 98 if the evap is at the front on the drivers' side in front of the LHS front wheel under the fender or at the rear just forward of the RHS rear wheel up under the floor. Either way these are known issues.

Neil.

Post by **scot850** » 22 Jun 2021, 14:16

Should also add it may be worth jumping the fuel relay to make sure it is not failing as it heats up.

Neil.

S Carlson · Post by **S Carlson** » 22 Jun 2021, 16:20

scot850 wrote: ↑22 Jun 2021, 14:15 Check your water temp sensor is working. It is a classic issue and will over-rich the fuel if not working correctly.

I can wiggle the plug and test with a multimeter, sure. But wouldn't this set a code? P0117, P0118, P0125 are all coolant temp sensor codes for high, low, and no-signal respectively.

Check fuel pressure when engine is warm. Could be the pump is dying but is ok when cold and seizing as it heats up.

It often happens right on startup, though. Then, turning the car off and back on again fixes it. So I don't know if it's correlated with how warm the fuel pump is. In fact, on long drives at speed, it never has a problem.

A major air leak would cause an issue especially with a turbo. Check all vacuum lines and the pipes from the air box to the turbo including for cracks in the intercooler.

Major air leak could be the evap system pipes have a crack in them at some point. Not sure on your 98 if the evap is at the front on the drivers' side in front of the LHS front wheel under the fender or at the rear just forward of the RHS rear wheel up under the floor. Either way these are known issues.

Right. I can check these easily and will do so when it's less rainy and hot around here! I am pretty familiar with the pipes and don't think they are cracked, but it's true that the intercooler's plastic end tanks could be cracked.

And yes, I'll definitely make a jumper for the relay, just in case something happens on the road to leave us stranded!

Post by **scot850** » 22 Jun 2021, 17:13

If this starts right from cold after starting it is more likely the ignition switch electrical position that is failing. I had a similar issue a few years back. If the ignition is the original it is high on the probable issue. Switching off and then re-starting clearing the issue would point to that.

Neil.

S Carlson · Post by **S Carlson** » 22 Jun 2021, 18:55

scot850 wrote: ↑22 Jun 2021, 17:13 If this starts right from cold after starting it is more likely the ignition switch electrical position that is failing. I had a similar issue a few years back. If the ignition is the original it is high on the probable issue. Switching off and then re-starting clearing the issue would point to that.

Neil.

Interesting. It does happen more to some drivers than others, and this could be explained by the different weights/sizes of keychains we have. I will have to try wiggling the key next time it happens.

However, it's not accompanied by any of the other symptoms (gauges going dead, turn signals and headlights not working, warning lights coming on). None of that stuff is happening. I'm not familiar with the way the car's circuits are set up. It may be that there's a set of contacts in the switch that only deals with the engine.

Post by **abscate** » 23 Jun 2021, 04:07

The electrical part of the ignition switch is isolated from the twisty part but they do last about 120-150k miles if used daily.

xanthefin · Post by **xanthefin** » 23 Jun 2021, 05:06

You mention Pxxx code which is standard OBDII and not any particular Volvo specific code as there is not always fault code for Pxxx / standard when there is a light or when there is fault code registered. Best to check modules each one where is the code if needs know it.

S Carlson · Post by **S Carlson** » 27 Jun 2021, 13:41

Well, I found one thing. The rubber hose that connects the plastic pipe that comes from the filler neck, to the charcoal canister.

Full service gas stations have a nasty habit of "topping off" which puts liquid fuel right into this hose, so it's no surprise it failed. I'll replace it with some generic fuel hose because the curve it follows is not that tight so I don't think I need any genuine Volvo pre-formed hose.

S Carlson · Post by **S Carlson** » 29 Jun 2021, 09:29

Replaced the hose today. It turned out that 5/8" was the correct hose size, even though the middle of the hose had shrunk to 1/2".

I used heater hose because it was what I had in my junkpile. I know it won't last long with fuel, but at least I can see if the CEL will stay off, or if other components need replacement also. I'm thinking that valve near the charcoal canister that this hose plugs into might also need replacement, since it's probably eaten its share of water and dust while the hose has been broken.

I had another pending fault, P0455, and pulled the flash-codes and got flash-code 1-2-2, but no logged (verified) faults. Is there a way, on these '98 cars, of telling which ECU the flash-code is coming from? I know on the older cars, you could just plug the pin of the diagnostic module into whatever socket, but on these newer cars where you pull the flash-codes from the OBDII port, is there a way to tell, for example, if the code is from the transmission versus the engine versus some other system?