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Discussion Starter · #1 ·
I drove my 1800ES on the Motherlode 400 this past weekend. Ambient temperatures were on the hot side - - - probably over 100F in some areas. Elevation ranged from around sea level to more than 9000ft. Water and oil temperature gauges indicated that the car ran relatively cool throughout the drive.

The car ran great on Saturday. On Sunday afternoon the engine started racing up to around 3500-4000rpm. I first noticed it at higher elevation - - - probably around 5000ft. I couldn't find an air leak, the throttle cable adjustment was okay, and the butterfly was working fine. It was still driveable, but I had to stay on the brakes descending due to no engine braking. I was hoping the problem was due to the elevation, but it continued even after we dropped down to 1000-2000ft.

I nursed it through to the end of the drive. After dinner, we started the 2.5 hour drive home. About 20-30 minutes later, the engine racing problem went away. It was much cooler at that time, so I started thinking that maybe the problem was due to heat affecting the fuel injection electronics. The engine ran fine for the next 2 hours, but about a mile away from home, the engine racing problem reappeared.

Any thoughts?
 

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Discussion Starter · #3 ·
That's a nice fuel injection trouble-shooting guide.

The coolant temperature gauge was reading normal throughout the weekend, but I'll take a look at the guide later today.

I did a quick skim while downloading that manual and I think my intake manifold is missing a ground strap.
 

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That's a nice fuel injection trouble-shooting guide.

The coolant temperature gauge was reading normal throughout the weekend, but I'll take a look at the guide later today.

I did a quick skim while downloading that manual and I think my intake manifold is missing a ground strap.
The temp gauge in the dash (and its sender) is not the component I am trying to identify.

The car has a sensor/sender that informs the control module as to coolant temperature thus having some affect/effect in engine rpm.

George Dill
 

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Uncommanded engine RPM is always, always, always, without exception, unwanted air getting into the intake, never, ever, ever, a fuel problem (sorry to be emphatic, but some people resist this notion). There is nothing in the injection electronics that can cause unwanted air, so that's not it. It only takes a very small amount of unwanted air to make the idle race when the engine is not under load -- the trick is figuring out where it came from, and I don't know how to do that if the problem cured itself.
 

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I am having a similar problem with a 73 ES project car. I have two massive vacuum leaks. The largest seems to be caused by the MAP sensor, on the right fender. I still need to do a test, try to blow through it and see if indeed it is causing the leak (car is off site, no access to it until next month). But I am almost certain that the little diaphragm in it gave. When I remove the hose and plug it, the rpm goes down to almost normal (then the other leak I have close to the throttle takes over).

It is somewhat of a miracle that the engine can run without a MAP, but it did run well with the MAP disconnected (but have not driven it).
 

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As for troubleshooting, next time it happens start pinching the different hoses that go to the manifold to see if you can slow the engine down. It might be that your cold start air valve got stuck open or something.
 

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Discussion Starter · #9 ·
Thanks for the great comments.

I think I'll check the brake booster first. I wasn't using the brakes much on the freeway drive home when the problem went away. But the racing came back when I got off the freeway onto surface streets.

I have another vintage vehicle event this weekend, so I won't be able to investigate for at least a week.
 

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Discussion Starter · #10 ·
I had to take a hiatus from troubleshooting due to some work travel.

Isolating the brake booster had no effect.

Running through the fuel injection troubleshooting guide:

Pressure Sensor
pins 7 to 15 = 90 ohms (spec = 90 ohms)
pins 8 to 10 = 345 ohms (spec = 350 ohms)
pins 7 and 15 to GND = OPEN
pins 8 and 10 to GND = OPEN
So the pressure sensor checks out OK statically, but would a torn diaphragm still cause problems?

Coolant Temperature Sensor
pin to pin = 2765 ohms (spec = 2100-3100 ohms)
either pin to GND = OPEN
So the coolant temperature sensor checks out OK.

Induction Air Temperature Sensor
pin to pin = 335 ohms (spec = 260-340 ohms)
either pin to GND = OPEN
So the induction air temperature sensor checks out okay.

Throttle Valve Sensor
I used the procedure where the stop screw is adjusted (1) turn CW after touching, a 0.020" feeler gauge is inserted under the stop screw, and a voltmeter is used to measure voltage between pin 17 and GND when the ignition is turned ON. Turning the throttle valve sensor CCW to the STOP position I measured 12 volts between pin 17 and GND, but specification is less than 5 volts. Do we have a winner? Phil states very strongly that high rpm is always an air leak problem, but the fuel injection troubleshooting guide seems to indicate that the throttle valve sensor can affect idle too. Also, any recommendations for finding a new throttle valve sensor? A search for the Bosch part number indicates that this is NLA?

I haven't been able to locate any cracked hoses, and all of my hoses are less than 2 years old.

What's the recommended procedure for ensuring the cold start air valve is working properly?
 

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The cold start valve is a fuel injector and would NOT be responsible for a fast idle. You may be thinking of the auxiliary air valve, connected to 2 hoses at the front of the cylinder head. It can stick open but ONLY starting from cold when it would normally be open. It is supposed to close when it gets warm so if it doesn't your idle will be somewhat high from startup, where it normally should gradually slow down as the engine warms up. This is probably not your problem. One thing that can mess up and then "fix itself" is the throttle butterfly. There are two possible problems with it: 1) it may have a spring-loaded "overrun valve" in it. If it does, take out the butterfly and solder the valve shut. 2) sometimes the screws that hold the butterfly plate loosen and allow it to shift a bit out of position. If it does that it will NOT close completely although the amount it stays open may seem slight. The cure for this is to work it back into its proper position where it does close completely and then tighten the screws CAREFULLY (but good and tight).
Sometimes the butterfly plate will vibrate back into a location where it can close completely.

You should check the MAPSensor with vacuum. If the vacuum dissipates it is leaky, and if it holds the vacuum it may be OK. Leakage is normally through a crack in the diaphragm. Normally if it leaks it will continue to do so and NOT fix itself. Only leakage should have a substantial effect on idle speed, not the electronics.

Your throttle valve "sensor" is actually a switch. It does two things: 1) it informs the computer when your foot is off the gas pedal that the engine is supposed to be idling and a somewhat diffferent mixture calibration is used, slightly adjustable by the knob on the back of the computer. 2) it causes additional trigger pulses to the injectors upon acceleration to temporarily enrich the mixture like an accelerator pump would do on a carbureted engine. You can check this by opening the throttle with the ignition on but the engine not running. You should hear a fairly rapid series of clicks from the injectors when you are opening the throttle but not when you are closing it. I think your TPS is probably OK.
 

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Discussion Starter · #13 ·
One thing that can mess up and then "fix itself" is the throttle butterfly. There are two possible problems with it: 1) it may have a spring-loaded "overrun valve" in it. If it does, take out the butterfly and solder the valve shut. 2) sometimes the screws that hold the butterfly plate loosen and allow it to shift a bit out of position. If it does that it will NOT close completely although the amount it stays open may seem slight. The cure for this is to work it back into its proper position where it does close completely and then tighten the screws CAREFULLY (but good and tight).
Sometimes the butterfly plate will vibrate back into a location where it can close completely.
My throttle butterfly does have an overrun valve. It shouldn't be very hard to temporarily seal that up with tape to test the effect. I inspected the butterfly valve fairly carefully, including checking the screws.

You should check the MAPSensor with vacuum. If the vacuum dissipates it is leaky, and if it holds the vacuum it may be OK. Leakage is normally through a crack in the diaphragm. Normally if it leaks it will continue to do so and NOT fix itself. Only leakage should have a substantial effect on idle speed, not the electronics.
I don't understand what you mean by "check the MAPSensor with vacuum". Can you please clarify?

Your throttle valve "sensor" is actually a switch. It does two things: 1) it informs the computer when your foot is off the gas pedal that the engine is supposed to be idling and a somewhat diffferent mixture calibration is used, slightly adjustable by the knob on the back of the computer. 2) it causes additional trigger pulses to the injectors upon acceleration to temporarily enrich the mixture like an accelerator pump would do on a carbureted engine. You can check this by opening the throttle with the ignition on but the engine not running. You should hear a fairly rapid series of clicks from the injectors when you are opening the throttle but not when you are closing it. I think your TPS is probably OK.
There is a switch in the throttle valve sensor assembly, but the assembly also includes a potentiometer that indicates the position of the butterfly plate. According to the fuel injection troubleshooting guide, my throttle valve sensor isn't working properly (see my 8/26 post). Of course that doesn't mean the throttle valve sensor is causing my high idle issue. But if it's not working properly, I might as well fix or replace it.
 

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Intermittent problems are always a headache. IMO about all you can do is be equipped to try and diagnose them the next time the problem pops up. Since you're looking for an air leak and one of the hoses leading to the manifold is a possible source, why not carry a small pair of long nosed vise grips with you at all times. Then if / when the probelm reappears you con pinch off the AAV, diaphram vacuum, PCV etc. hoses one at a time to see if there's any change. If none of them seems to be the cause, then you'll know you're looking for a leaking seal. Given that it reversed itsself, my (semi-educated) guess would be the AAV getting hung up. But I'll be interested to hear what you find.
 

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Discussion Starter · #15 ·
1800ES Fuel Line Size

While troubleshooting my high idle issue as detailed here:

http://forums.swedespeed.com/showthread.php?176575-1800ES-Engine-Racing-up-to-3500-4000rpm

I discovered that some of my fuel injection lines were leaking. Not a good thing when the fuel rail is located directly above the exhaust manifold. . . .

I removed the fuel line that ran from the fuel rail to the cold start valve for reference and bought some 1/4-inch / 6.4mm fuel line that seemed to be about the same size. However, when I tried to fit the new line, I discovered that the ID is too small.

None of the current fuel lines are marked, but I'm guessing that somebody replaced at least some of the fuel lines with non-fuel-injection type lines that stretched over the fittings more easily.

I've surfed the archives and Google for 30-45 minutes but can't find anything that tells me the correct diameter for the fuel lines. This would include:

*fuel rail to cold start valve
*fuel rail to pressure regulator
*fuel rail to injectors
*fuel supply to pressure regulator
*fuel return from fuel rail

Any recommendations as to the correct size? And can I get these from NAPA, O'Reilly, etc.?
 

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Discussion Starter · #16 ·
I e-mailed a friend with this same question, and he responded that the lines are 5/16" which is pretty much identical to 8mm, which is what I'm assuming the original lines were.

He recommended inspecting a section of fuel line under the car, approximately under the driver's seat. And also the lines around the fuel pump in the rear.
 

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They are all 5/16" except for the large hose between the tank outlet and the pump inlet. Don't remember what that one is, but there's no pressure on it.
 

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Discussion Starter · #18 ·
Throttle Position Sensor (Flap Contact) Testing

While troubleshooting a high idle problem on my 1800ES, I checked out all sensors related to the fuel injection system per the Volvo Fuel Injection Fault Tracing guide here:

http://volvo1800pictures.com/document/fuel_injection_fault_tracer/fuel_injection_fault_tracing.pdf

Starting at page 2-31 there is a procedure for checking functionality of the throttle position sensor, which is referred to as a "flap contact' in the troubleshooting guide.

According to the guide, when rotated counter-clockwise, the throttle position sensor pin 17 to GND should be 0 volts, and if pin 17 to GND is greater than 5 volts, the throttle position sensor should be replaced. I read 12 volts between from pin 17 to GND on my throttle position sensor.

I don't think the throttle position sensor is contributing to my high idle condition, but the fault tracing guide says this component is defective and should be replaced.

Before I run off and buy what is likely an expensive part, I wanted to double-check to verify the fault tracing guide diagnosis procedure and voltage levels is correct.
 

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Discussion Starter · #19 ·
Closing out this thread. I bought 9ft of 5/16" fuel injection line at NAPA and replaced all of the fuel lines using correct fuel injection type hose clamps. No leaks. At least some of the old line that I removed did not appear to be fuel injection line, so somebody had been in there previously and mucked things up.

Major annoyance for this work was calling auto parts stores (O'Reilly, Pep Boys, and Auto Zone), asking whether they had 5/16" fuel injection line, being told "yes we have that", asking if they were *positive* that the line was fuel injection line and not standard fuel line, getting a reply of "yes we're sure", and then driving to these stores only to discover that they did not in fact have fuel injection line. Minor annoyance was buying a box of what were supposed to be fuel injection hose clamps from NAPA while I'm buying the fuel injection hose only to discover that the clamps were standard worm type hose clamps when I got home. It's crap like this that can turn a 2 hour task into a half-day endeavor.
 

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Discussion Starter · #20 ·
I got a little distracted when I discovered a couple of fuel leaks on my fuel rail. I wound up replacing all of the fuel lines with new fuel injection type line. It appears somebody had been in there at some point in the past and used standard fuel line rather than fuel injection type line. Luckily I caught it before there was a fire.

Anyway, back to my high engine idle. . . . .

It appears the auxiliary air regulator aka auxiliary air valve might be the culprit. Surfing a bit on Google indicates that this component is somewhat notorious for failing in the OPEN position resulting in high engine idle. I live in California, so I think I can live without it, so I'm disabling it by plugging up the lines on the intake manifold. At least for now.

I replaced the hose going to the pressure (MAP) sensor as it was starting to crack at the end.
 
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