High idle issue

Tiny
NEIL SHEEHAN
  • MEMBER
  • 1996 VOLVO 960
  • 2.9L
  • 6 CYL
  • RWD
  • AUTOMATIC
  • 180,000 MILES
So, bought this car recently. Been going down the line fixing everything. Started with an audible vacuum leak at the intake hose boots, loping high idle issue, and a cylinder one misfire. Smoke tested and tested various components, then replaced the intake manifold gasket, the intake boots, cracked oil trap, spark plugs, coil wires, idle air control valve, some random cracked vacuum hoses, and the second stage ignition module. I still have a miss, I need to finish replacing the last few coil wires. But my biggest issue is I still have a 1250 rpm's idle in park when warmed up, idle starts around 950 rpm's cold. It also wont hold an rpm with the gas pedal, if you push the throttle down slightly the rpm's go to over 4000 rpm's within a few seconds, though the throttle position sensor reads only twelve percent. No check engine codes. And I got all the monitors to run. I have adjusted the throttle closed, throttle body is clean, smoke tested engine no leaks. I have tested the throttle position sensor, it is at.55 volts closed and 4.3 volts open, which is a bit off on the full open value but would not explain my idle. The absolute throttle position reads 9.8% at idle. Fuel trim always reads within a few percent of zero. I am just stumped. I am leaning towards the MAP sensor because the numbers do not add up, but I' am stumped on how to test it currently, had to call Volvo to even find it because it does not run off vacuum? My vacuum gauge reads twenty inches of mercury at idle off the manifold, I ran some of the normal vacuum gauge tests, all normal. Map sensor reads thirteen to sixteen inches on my scanner, I am at sea level.
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Friday, November 4th, 2016 AT 2:11 PM

24 Replies

Tiny
JIS001
  • EXPERT
Check your engine coolant temperature sensor reading. If it is always reading cold the computer will race the engine to try and get it to reach normal operating temperature. Also since the engine is racing it will dump a lot of fuel which could cause a misfire and sometimes even a hard start. If you have had a hard start also, remove the spark plugs. They get fouled out with raw gas. Drying them up will get you started faster.
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Friday, November 4th, 2016 AT 5:49 PM
Tiny
NEIL SHEEHAN
  • MEMBER
Coolant temperature sensor reads room temperature when cold and warms up to 219 degrees within five minutes. The idle never lowers once it gets warmer, in fact it gets gradually higher. The plugs are not fouled and fuel trims are within a few percent of zero, so computer is neither pulling nor adding much fuel. I just tried replacing map sensor with a junkyard unit as a test, car acts exactly the same.
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Friday, November 4th, 2016 AT 6:23 PM
Tiny
JIS001
  • EXPERT
The computer has default values if there is a problem with the signal. Back probe the ECT sensor and let me know what the voltage reading is from cold to when it warms up.

Here is a description of how the ECT sensor operates

The engine coolant temperature (ECT) sensor supplies the engine control module (ECM) with a signal describing coolant temperature. This gives the engine coolant temperature sensor a measurement of engine temperature and influences the control of:

injection period
idling speed
engine cooling fan (FC)
ignition timing
on-board diagnostic (OBD) functions.
The sensor incorporates a temperature-sensitive resistance with a negative temperature coefficient (NTC). The sensor is supplied with a stabilized voltage of 5 Volts from the engine control module.

The voltage across the sensor is a function of the engine temperature and, therefore, of sensor resistance. Voltage can vary between zero Volts and five Volts.

The engine control module uses substitute values if the signal from the engine coolant temperature sensor is missing or faulty, however, substitute values can cause starting problems in very cold weather.
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Friday, November 4th, 2016 AT 9:14 PM
Tiny
NEIL SHEEHAN
  • MEMBER
So, finally had time to check it. Coolant temperature sensor starts at 1.67 volts then drops to about 1.3 volts in the first few minutes, then it shoots up to 3.9 volts. Over about five minutes it settles to 2.58 volts, then after a few more minutes of sitting at 2.58 volts. It suddenly starts dropping again slowly to about 1.89 volts when engine fan kicks on finally. It rises to around 2.1 volts. This seems to be closed loop operation from this point. I hooked up my big shop scanner, and I have no OBD codes, but I have the Volvo specific code 233 for long term idle air trim. What do these voltage values mean? I am used to a linear increase or decrease of voltage.
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Sunday, November 6th, 2016 AT 6:31 PM
Tiny
JIS001
  • EXPERT
Is the code for upper or lower trim?
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Sunday, November 6th, 2016 AT 7:46 PM
Tiny
NEIL SHEEHAN
  • MEMBER
Unfortunately, that's all it gives. I have a launch brand scanner, it uses Google for code definitions, and searching for code 233 long term idle air trim returned nothing. For now, I ordered a coolant temp sensor, as it obviously has issues. I ohmed it out too on top of the issues it had with the voltage test. It has infinite resistance cold, around operating temp its at 160 ohms.
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Monday, November 7th, 2016 AT 10:50 PM
Tiny
NEIL SHEEHAN
  • MEMBER
I'm guessing the code 233 is because I have the throttle body adjusted to absolute minimum with the idle being abnormal. If you take off the filter box and put a single finger over the intake, the idle lowers a little and tries to die, 2 fingers usually kills it. Hopefully the coolant temp sensor helps bring my idle down to earth and I'll readjust the throttle screw a bit if needed.
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Monday, November 7th, 2016 AT 11:08 PM
Tiny
JIS001
  • EXPERT
Here is the DTC definition for your code

Trouble Code Conditions
If the idle air trim adaptation is allowed to increase (upper limit: 22 kg/h (10 lb/h)) or decrease (lower limit: 8 kg/h (3.5 lb/h)) the volume of air through the valve by too much to maintain the correct idling speed, diagnostic trouble code (DTC) EFI-233 is stored.
Substitute value(s)
None.
Possible source(s)
Upper limit:
Blocked air cleaner (ACL) or air intake.
Contact resistance in terminals.
Incorrectly adjusted throttle body.
Defective idle air control (IAC) valve.
Lower limit:
Air leakage.
Contact resistance in terminals.
Incorrectly adjusted throttle body.
Defective idle air control valve.
Fault symptom(s)
Idling speed too high or low.

Also try reseting all adaptations except for the flywheel adaptation using your Launch scanner after you replace the ETC sensor.
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Monday, November 7th, 2016 AT 11:21 PM
Tiny
NEIL SHEEHAN
  • MEMBER
New ECT sensor made no difference. I don't have scanner with me, I'll just disconnect the battery overnight and let it idle in the morning and see if it relearns anything. When I checked on my scanner last, the only special function had to do with the seat memory and two other unimportant things. Nothing I can recall about unlearning/resetting anything. Back to square one possibly. Voltage drops normally on the new sensor. So I tested my iacv, pins 1-2 have 13.1 ohms, specs is 15, so good there, plus I checked it's action, it opens and closes normally. But I just tested the mass airflow sensor, as it's one of the only things I haven't tested for some reason. Between pins 2-3, I have 212000 ohms of resistance. Sooo. Yeah. Did I look up the test procedure right? . !
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Tuesday, November 8th, 2016 AT 10:28 PM
Tiny
NEIL SHEEHAN
  • MEMBER
By the way, thanks for the help thus far!
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Tuesday, November 8th, 2016 AT 10:29 PM
Tiny
KEN
  • ADMIN
Please let us know what you find so it will help others.

Best, Ken
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Wednesday, November 9th, 2016 AT 9:18 AM
Tiny
JIS001
  • EXPERT
I dont have a resistance spec for that. Just what it needs to read at idle. Have you checked your throttle for leakage also? Spray some carb cleaner around it to see if the idle drops down. Also try doing a soft reset by disconnecting the battery terminals and touching the leads together for 15 minutes.
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Wednesday, November 9th, 2016 AT 9:57 AM
Tiny
NEIL SHEEHAN
  • MEMBER
I smoke tested the car. I had smoke come out of the throttle body return spring but theres no stopping that. I'll test the maf. I've smoke tested the intake tube as well, no leaks. I had the battery disconnected last night, I'll do the ecu reset with the cables.
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Wednesday, November 9th, 2016 AT 10:18 AM
Tiny
JIS001
  • EXPERT
If you spray it down with carb cleaner and it really is leaking you should notice a change in the idle.
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Wednesday, November 9th, 2016 AT 11:49 AM
Tiny
NEIL SHEEHAN
  • MEMBER
Just for argument's sake, I tried again with the brake cleaner. Still had some dirt around anyhow. Cleaned it off, then 15 seconds later my idle went down to 700 Rpms and stayed there for well over 5 seconds. It was odd, idled lower like it should. I then used an entire can of brake cleaner trying to replicate it but I was unsuccessful. Also, Maf sensor reads 1.24v at idle but should be at 1v. Also that chart you sent says maf should read 16 kgh, I have about a pound per minute reading on my scanner which equals 60lb hr or 27 kgh according to my math. So I'm running about roughly double the air I should through my maf? But idle is high, so that value is skewed. But still. Soft reset unsuccessful as well. I'm not sure how to test most of the other items on that chart as my scanner doesn't show values for them.
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Wednesday, November 9th, 2016 AT 2:41 PM
Tiny
NEIL SHEEHAN
  • MEMBER
Update, I finished my coil wires after my cars idle shot up to 1500-1900 rpms. My cat started to glow a bit. I still have a miss/stumble but my knock sensors dont register it anymore. Idle went back to previous amount but it still has a high metered flow reading on the maf sensor and the iacv is closed fully. Acts like a vacuum leak, but can't find one, and the extra air is metered, not unmetered. Is the computer changing the maf sensor values?
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Thursday, November 10th, 2016 AT 9:11 PM
Tiny
JIS001
  • EXPERT
The reading could be caused by the high idle. Kinda odd the idle did actually go down for a bit? It would sound like you have a vacuum leak somewhere? Also what brand idle air control valve did you install?
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Friday, November 11th, 2016 AT 1:24 PM
Tiny
NEIL SHEEHAN
  • MEMBER
I have verified the valve is fully closed at idle. It's a Volvo iacv, but it's rebuilt. It was running so rich the cat couldn't keep up and the rear 02 started reading like the front. I removed a huge 2 inch air hose from the intake and it still ran. I could feel pressure pulsing through the intake tube. The idle got so bad I removed the entire manifold, I found a large piece of debris stuck in one of the valves on cylinder 1. I tried removing it with a magnet, but it was non magnetic, then tweezers but eventually it fell in. I'm not sure how that can make it run rich, but we will see.
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Friday, November 11th, 2016 AT 6:12 PM
Tiny
KEN
  • ADMIN
Yes it will, if you have combustion getting into the intake system it will cause the o2 sensors to think the exhaust is lean and try to richen it up. Do a compression test once completed to see if the engine needs a valve job.

Here is a guide.

https://www.2carpros.com/articles/how-to-test-engine-compression

Best, Ken

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Saturday, November 12th, 2016 AT 12:22 PM
Tiny
NEIL SHEEHAN
  • MEMBER
Thanks, yeah, after I put cylinder 1 as close as I can get to TDC with the valve open I'm going to blow it out with compressed air to get the debris out the exhaust, I'm going to visually inspect the opening and closing of all valves, then I'm performing the compression test to verify. A better test to check valves is a cylinder leakdown test rather than the compression test fyi. Just some helpful advice, no offense! Thanks for all the help guys, car is being hateful.
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Saturday, November 12th, 2016 AT 1:25 PM

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