Car intermittently failing to start (low idle)

Question

I have a Volvo 850 that is intermittently failing to start. When the starter is activated, the car sputters at a low idle (500 RPM) then conks out. Pumping the accelerator has no effect.

So far the problem has only occurred after a short trip. For example, I will go to the store and when I come out, the car sputters and will not start. It has never happened when the car has been sitting for a long time.

In all cases so far the car has always started after some delay. For example, the first time it happened, I tried for about 5 minutes to start it with no luck, then I went and talked to someone for 45 minutes and the car started. The most recent time it happened, I went to the grocery store, then went to another store a short distance away and then the car would not start. I tried for 10 minutes with no luck. Then I had lunch, read a chapter of a book, and then the car started about 30 minutes later.

I suspect that the problem is either that the fuel controller is failing or the fuel pump is failing, but I do not know how to discriminate between the two.

How can I further diagnose the problem?

Answer 1

I think this is a fairly common problem, over 370,000 results on Google.

I have posted a couple of links with possible solutions, which ones have you tried?

https://blog.fcpeuro.com/3-reasons-a-volvo-850-s70-wont-start

https://www.ericthecarguy.com/kunena/10-Repair-Central-The-How-To-Forum/40074-volvo-850-starting-problems

https://www.thevolvoforums.com/threads/volvo-850-turns-will-not-start.7654/

https://www.youtube.com/watch?v=2x3W3jPv_hs

https://www.youtube.com/watch?v=3pL-tjDMpnE

https://www.youtube.com/watch?v=ifXrq8gakTQ

https://www.youtube.com/watch?v=2x3W3jPv_hs

https://www.youtube.com/watch?v=3T2r0NJT9oY

https://www.youtube.com/watch?v=gLoO-D4yOcU

https://www.youtube.com/watch?v=jz6AtBHViv8

https://www.youtube.com/watch?v=gLoO-D4yOcU

https://www.youtube.com/watch?v=ifXrq8gakTQ

https://www.youtube.com/watch?v=x3MP9KaPMqA

From everything I have read, this vehicle hates short trips or turning it on for short periods of time and then switching it off!

When I am less short on time, I will watch and carefully read the links and list what you need to do in an attempt to resolve the issue

Answer 2

Are there any fault codes stored, and does the CEL go away under prolonged starting?

You can use a fuel pressure gauge to rule out both your fuel pump and pressure regulator. Attach and watch it when it's refusing to start next time. There's a convenient valve on your fuel rail for that, same as a tyre valve, so even a chap tyre pressure gauge could perhaps be used. (but maybe it won't live long after) You should see around 3 bar(44psi) of fuel pressure when starting. If it's lower than that can indeed be the cause of the problem.

Check your compression, low compression will make it hard to start, possibly refusing to do so at all when any other minor issue arises.

(via OBD, cheap readers suffice here) Look into the long and short term fuel trims if you can, it will give more insight in what has happened before.

It's possible the MAF is contaminated, causing it to run roughly. Some MAF's heat up very hot when you're shutting off the engine, burning off some of the dirt. That may be why you can start it again when trying it a while later.

Check for air leaks, they will cause lean running, or no running at all.

Answer 3

My money is on a temperature sensor, either IAT (probably part of the MAF) or the ECT.

The car won't start after a heat soak.

The previous answers all point to more OBD PID examination, which would make my idea obvious as well as a whole host of others.

Also, have you replaced the fuel filter? Sometimes a car will restart after the debris "falls away" due to the pressure dropping. How is the car on long trips?

Answer 4

After working on this problem more, I have the following advice for somebody with the same warm start problem:

1. When a Volvo 850 idles low and will not start intermittently when warm it is probbably not the fuel controller or pump. It is probably the idle system that is failing. Note that 1990-era cars will NOT USUALLY GIVE CODES WHEN A SENSOR FAILS the way a newer car will.

2. If the fuel tank just got filled and it fails to start it is the fuel purge valve.

3. If the car has trouble idling or stalls out on start, but runs when the accelerator is pressed then it is probably a sensor (MAF or atmospheric or coolant temperature). If the problem is with the MAF, it can be tested by unplugging the MAF and trying to start. If the car starts, then the MAF is dirty. If it is not the MAF, then it is the atmospheric sensor or the camshaft sensor or the coolant temperature sensor.

4. If the car has erratic idle and behaves incorrectly when the accelerator is used, then it may be the throttle body position sensor, which is a potentiometer attached to the the throttle body valve.

5. If the car idles low and does not respond to the accelerator (my situation), then the idle air control valve is dirty and needs to be cleaned. What is happening is the pintel inside the IACV is getting stuck.

6. If the car idles normally, but will not accelerate, put the car in park and open the hood with the car running and lift the lever on the throttle body. If the engine engine does not acclerate, then the throttle cable is slipping.

7. Warm start issues are usually not caused by the fuel controller, but you can test the controller by carrying a jumper wire in the car and a T25 driver. The jumper wire is 3 inches of 16-gauge wire with a 16-gauge (BLUE) spade connector crimped on to both ends. When the problem occurs, unscrew the lid of the fuse box using the driver to get access to the relay tray. Pull relay #103. There are four slots, top and bottom, left and right, in the socket. Connect the top and bottom slots. This will cause the fuel pump to run constantly. Try to start the car. If it starts, then you have a bad fuel pump controller.

8. Most other problems are not intermittent, or throw codes. For example, fuel pumps usually do not partially fail. They usually fail without warning and the car stops. Also, a vacuum leak will almost never be intermittent.