Popping/backfiring sound when idling

[gnalan]

I borrowed a compression tester, but haven't had time to check the engine to see what it shows. I know with cars that use a throttle cable you hold the throttle all the way open with the gas pedal. How do you hold it open with an ETM? Does it need to be fully open to get accurate readings, or is pulling off the elbow from the ETM to the MAF enough to let enough air in? If I'm only needing around 250rpm to crank the engine over to get the readings, I wouldn't think it needs to be open all the way. I'm sure VIDA would tell me, but I haven't had time to throw the DiCE on it to see what the recommended process is.

[gnalan]

Check compression. Maybe you have a bad valve leaking back.

Compression numbers:
Cylinder 1, 192psi
Cylinder 2, 190psi
Cylinder 3, 192psi
Cylinder 4, 191psi
Cylinder 5, 189psi

Tested back to back, with the battery on a charger. I went from 1-5, then 5-1, cranking the engine over until the extra dash lights went out (about 9 or 10 revolutions). Those numbers are from the 5-1 pass, which were almost the same as the 1-5 numbers. I also held the gas pedal to the floor, but I don't know if that had any effect or not on the throttle position. I didn't have anyone to hold it open, and didn't want to put something in it to hold it open and then have to chase it through the intake if it got sucked in.

I was going to do a wet test too, with a little oil added to the cylinders, but from those numbers I didn't think I needed to.

I think I read somewhere that the ETM's that were replaced came with a yellow label, but I could be wrong. Mine is still a white label, and I think still the original one.

[gnalan]

Taking all of that apart, and putting it back together afterwards didn't change anything. Still having the popping sound that I can hear, and feel with my hand on the air box. Idle is still hunting around, and the stalling/stumbling problem is still happening too.

From the compression test, it looks like everything is ok with the valves. I don't have an air compressor to borrow a leak down tester to check the head/valves with.

Does this confirm that the ETM is bad, or should I look for some other problem?

[cn90]

So, that is good news with no burned valve issues, which usually condemn a car with this mileage (the fix is not worth it at 186K etc. etc.).

I understand that you had this problem after filling with Sunoco gasoline and now you use another gas station.

In the 1990s, my sister's Honda Accord had gasoline contaminated with water.
It took many weeks and months to figure it out. The water just stayed in there for weeks and months causing misfires.
Finally they drained the tank and pumped in new gasoline.

In your case, you can access the gas tank from the sender unit that you removed/fixed recently.
Get a long hose and a syringe, dip the tip of the hose to the bottom and suck out some 50 cc into a clean jar.
If there is water, it will settle to the bottom assuming the mix containers some gasoline-H2O mixture.
Now you can see the water line below the gasoline line.
If you suck out only H2O, then you will not see the interface.

[gnalan]

I'm afraid to take the sending unit back out since I finally got the leak to stop, and don't really want the leak coming back.

Is there another way of doing this? I'm assuming the fuel pickup pulls from the bottom of the tank, unless it floats around with the gas level. Could I do what I did when I did the fuel pump, and take the Schrader valve out of the fuel rail, hook up a hose with a clamp so it doesn't leak everywhere, and pump some out that way? I have a red 5 gallon plastic gas can I used last time, but I wouldn't be able to see if there's water mixed in with the gas using it.

I can try and find some glass Mason jars to use, and fill up several of them. Then if some/all have water in them then I'll try to figure out what to do with the bad gas. If there's no water, what else could be my problem?

I'm pretty much lost at this point. I'm used to older cars with straight sixes, a Rochester single barrel carb, no airbags, or anything run by a computer. A whole lot easier to work on, and a lot cheaper.

[cn90]

Get some empty windshield washer container so you can see.
Just clean them with water and dry them in the sun.

Pump via the Schrader valve, remove the valve core, the jump the fuel pump.
Forgot the procedure, but it is somewhere in forum.

[gnalan]

I didn't even find the fuel relay until today. When I replaced the pump I just removed the fuse from the left side of the dash, number 33.

I removed both the fuse, ran the car until it died, then found the relay and pulled it after all 5 plugs were wet and smelled like gas when I removed them.

I couldn't hear the pump running with the fuse out, but I went ahead and pulled the relay to make sure gas wasn't still getting into the cylinders and messing with the compression test.

When I used the pump to drain the tank before, when I was replacing the pump, I took the valve out and just kept cycling the key on and off to get the gas out. It killed my battery, and I had to replace it with a new one. If jumping the relay will work better, I'd rather do it that way.

[EngineeringBloke]

You mention:

I have seen a difference in VIDA between the desired throttle position and the actual throttle position. Desired value stays at a fixed number, while the actual value is all over the place. Could this be my idle problem, and what's causing what sounds like backfiring through the intake? What would cause the two values to be different, and the actual value to jump around like it is? I'm hoping it's an easy fix, possibly a TPS problem, rather than a bad intake valve/spring or worse. Maybe a wiring issue somewhere? Would that cause my problems?

When the ECU is controlling the throttle, it tells the throttle motor to position to a certain opening (rotation). And a spring helps close the throttle plate.

The throttle position is changed to adjust (set) the amount of air coming in.

When the ECU is trying to set a fixed open position, BUT the throttle plate is reporting that the plate is varying in position, then the throttle has failed. It is not responding to the commands correctly.

This is the typical failure of the 2000, 2001 throttles when its position sensor is worn. NOTE, another internal throttle module failure could cause this issue but is much less likely.

A replacement throttle will typically have a contactless position sensor that is more reliable.

1. Xemodex has info and parts but is spendy.
https://xemodex.com/us/electronic-throt ... -services/

2. Volvo OEM throttle is likely very spendy.

3. There is a kit on Ebay that replaces the contact sensor with a contactless one. You would need to open the throttle module. Not sure how easy the repair is but it looks doable. Search Ebay for

FOR SALE 99 00 01 02 Volvo ETM Contactless Throttle Body Position Sensor TPS Kit

. This kit does not require software loading as only the sensor is changed. Once the throttle module is opened for the repair, you can check the sensor and see if it is badly worn.

4. Or you could get an aftermarket throttle body module. (I got an aftermarket unit for my 2006 but mine has no software in the throttle unit.) However, I think that your year requires that the replacement have software loaded for it. I am not sure what would be involved with that. Yagger is a go to guy on this web site for this type of issue.

[EngineeringBloke]

Perhaps Volvo made its throttle module error detection less sensitive in order to get more life out of the module for their owners. However this may result in loss of detection of failing units. May be why you are not seeing a throttle failure CEL.

[gnalan]

https://www.volvopartswebstore.com/prod ... assemblies

Here's a new ETM from Volvo, which is cheaper, but I'm assing it won't last as long as the XeMODeX unit will. Plus the new Volvo ETM would need to be programmed. The cost for the VIDA subscription and the software added on top of that would end up costing more then the XeMODeX ETM. I can't afford either one.

I'm assuming trying a used one, with the correct software already installed, that it wouldn't last very long. Not sure what to do, but I need to fix it ASAP.