Idle/Power Problems? Troubleshoot Here

[echase76]

I have been noticing a lot of threads this winter relating to rough/surging idle, dying or intermittent power loss. Could it be the cold winter? Maybe. Could it be the fact that these cars are over 15 year? Probably. Anyway, due to all the threads I wanted to compile a list for troubleshooting.

Note: Many of these issues will NOT throw a code.

If your car is having these issues here is where to start:

Vacuum leak (start with elbow on passenger side of manifold and go from there)
MAF (start by cleaning)
Fuel Pump Relay (test by jumpering)
Clean Throttle Body
Clean Idle Air Control valve
Fuel Pump (test fuel pressure)
Spark plugs, Wires, Cap, Rotor

Less likely:

Ground Cables
Throttle Position Sensor
Engine Coolant Temp sensor
Brake Booster
Battery

If you own a 1999 or 2000 :

All the above plus ETM
B+ cable

This is not all inclusive, so please ADD to this thread or make suggestions.

If you have solved your issue please post the resolution here!! BTW my issue was solved with a new MAF.

[E Showell]

My fluctuating idle at stoplights disappeared after remanufacturing of the cylinder head to replace all valve stem seals, regrind all valve seats and replacement of both exhaust valves in the cylinder with the burnt valve (#3, incidentally). Idle is rock steady now.

[Ben850]

My fluctuating idle at stoplights disappeared after remanufacturing of the cylinder head to replace all valve stem seals, regrind all valve seats and replacement of both exhaust valves in the cylinder with the burnt valve (#3, incidentally). Idle is rock steady now.

Hmm... That sounds like a pretty simple $800. or so fix.

Unfortunately, I dealt with these issues earlier this year, and it was time for most of the items in the first list i.e. wires, rotor and cap.
All is well now, but I am glad I was working around the distributor area or there would still be another ghost.
What I did come across, was a cracked connector to the cam position sensor. This was the likely culprit in the wet weather issues. (Aside from 20 year old plug wires.)

Original'93 CPS.

I am sure this did not like water much.

[sunnyrollins]

Agree with E Showell, I went through most of the list at the top and I have to now hire someone to get the cylinder head removed and valves fixed. Very puzzled what did this so quickly, I have 136K... taking into a smaller local shop this week to see if I can save it. Beyond my abilities.

[E Showell]

Possible culprits -- running cheap regular grade gas (particularly in a hot climate), not keeping up with recommended oil change intervals, leaking valve stem seals and failed front O2 sensor or any combination of the above. Did you replace the front O2 sensor at 100K miles? If not, it would be a good idea to do so now with a Bosch unit.

[mtd240]

Possible culprits -- running cheap regular grade gas (particularly in a hot climate), not keeping up with recommended oil change intervals, leaking valve stem seals and failed front O2 sensor or any combination of the above. Did you replace the front O2 sensor at 100K miles? If not, it would be a good idea to do so now with a Bosch unit.

E Showell - could you expound on these a little further? I realize that higher grade gas will resist detonation/pre-ignition, since it isn't as unstable ("flammable"). Is this your reasoning for using a higher grade? I had thought the 850's FI system was complex enough that it could handle tuning for a lower octane gas.

Also - are there any symptoms for a front O2 sensor failure, or are you saying that at ~100k miles the 850 O2 sensor is usually responding much slower than it should?

[E Showell]

I am a shade tree mechanic at best so my understanding of the above is based largely on what I have read and a bit on personal experience. With those grains of salt: 1) cheap gas -- as with most things, you get what you pay for. Name brand gas generally is formulated with some solvents that will help maintain the fuel system. They are getting run through with every tankful, so if you use high quality fuel you shouldn't need that bottle of Techron every now and again. Regular gas -- notwithstanding computer mapping to compensate for lower octane, there's still a greater risk of detonation with lower octane gas and that isn't good for the valves. I understand that is worse in hot summer temperatures. 2) Running extended oil change intervals -- dirty oil can contain deposits that will coat your valves and hold heat on the valves when you don't want it too thus weakening/burning the valve over time; 3) valve stems seals -- I have my own theory that these simply wear out with age due to aging/degrading rubber and protracted exposure to high temperatures in a pretty hostile environment. I am not aware of folks changing valve stems seals on a regular maintenance schedule since it would be a hugely expensive job to tear into the engine just to do the valve stem seals, but I'm betting it would extend engine life considerably, all other things being equal -- [this is at best a theory and completely untested]; 4) 02 sensor, particularly the front one is a maintenance item at 100K miles. They should be changed in pairs -- i.e., front and rear, although the rear may be less critical if you can only afford to do one at a time. You won't necessarily get a check engine light as the front sensor is failing. It may depend on the mode of failure. Mine went after 229,000 + but, I believe, took an exhaust valve with it. I believe the failure mode was lean running -- the only really perceptible symptom of which is great gas mileage, by the way. Here I was thnking I was really outsmarting the world and driving with such awesome technique that I was squeezing every mile out of every drop of fuel. In truth, what was probably happening was progressive leaning of the mixture -- but not enough to set any codes -- as the front O2 sensor failed and engine temps getting hot enough from the lean running to induce excess engine heat and burn a valve. This theory has not been confirmed, but everyone I've shared it with says it is plausible.

I had heard, and Justin, for one, will advise that his O2 sensor failed by enriching the mixture -- which will give decreased fuel mileage and perhaps driveability issues. Decreased mileage you may well notice -- and figure it is worth investigating -- before any failure mode. Increased mileage, not so much -- you'll just feel inexplicably lucky. . . until things fall apart.

By all means, change at least the front O2 sensor if you are past 100K and are not sure whether it has been done before. It takes 5 min. and may well save you an engine, or cylinder head rebuild.

[abscate]

Summary of poor idle, okay above 2000 rpm thread on 1999 V70 T5 with Electronic Throttle Body (ETB)

After a radiator replacement job, car ran well for a day, then irregular missing and hard starting. 2 Hz cycle of swinging between low (350rpm) and normal rpm at idle.

Throttle above 2000 rpm was smooth, power ok but anemic.

After a lot of diagnosis failures I found a loose turbo hose at the top of the intercooler was the problem - the flow through the Mass Air Flow (MAF) sensor and the ETB was thus loosely correlated leading to hard running.

The engine would through a bunch of error codes and light the MIL (engine light) but these would self-clear so this didnt help the diagnosis.

[donis222]

When I was young, cap, plugs and wires were wearing out regularly. Today, Volvo does a great job of securing the wires in order that they don't flex and keeping the temp down in the engine compartment. I never think of those 3 as the culprit for at least 100k miles. Take the cover off and look for sparks at night. spray a very little water on them and listen for change. Change the coil wire as it flexes a lot.
Vacuum first and foremost. no gauge use spray start (careful fire) or propane to try and find a leak, but I went a long time trying not to buy a vacuum gauge, then I got one a life changed.
Pull injector wires off, one at a time. Feel the injectors for abnormal click.
When in the junk yard, I pick up the wire harness connector ends of all important sensors, in order to be able to plug them into the sensors, connect my meter and test them. Troubleshooting is a breeze now.

[98T5]

Don't forget to clean the TPS (Throttle Position Sensor) and IAC (Idle Air Control Valve). most neglected.