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1970-1995 Range Rover Classic
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42 Posts
Discussion Starter #1 (Edited by Moderator)
Hi all,

My 1990 RRC had been experiencing a rich running condition so used the RAVE to evaluate codes that popped up on the display. Initially, I had a code 17 and when I checked the throttle position sensor the idle position voltage was reading low. I adjusted the TPS in it's "ears" and got it into range and the code 17 cleared. Next up was code 44 for the driver's side O2 sensor. I ordered a couple of sensors and while I waited, I checked the voltage, resistance and amperage on the other fuel injection components. Everything was in spec.

When the O2 sensors arrived I replaced both. Immediately on start up I noticed that the exhaust was much leaner and with a 100 mile trip verified that mileage was back up around 12 mpg from about 10 mpg. After driving for any period of time I am continuing to get codes 44 or 45 (driver's or passenger's side O2 sensor) I realize this is likely due to a vacuum leak, so I've been searching to see if I can find it. I have taken the stepper motor out and slapped it around a little - but it seems to be giving good IAC service in any event. I've pulled the vacuum lines off of the plenum and plugged them to see if I get any difference. I still get the O2 sensor fault codes. The truck idles great most of the time, and pulls a steady 18" of vacuum at idle.

What I have experienced is that once the truck is up to operating temperature the idle will stumble briefly with the idle dropping from 750 rpm down to about 300 and then will hunt while it tries to recover. It will eventually recover, but it will do this stumble routinely when driving around - especially when coming down from highway speed to a stoplight etc.

I converted this truck to a Pertronix distributor and coil some time ago - eliminating the amplifier and stock distributor issues.

What's interesting is that the idle issue doesn't occur until the thermostat opens (engine reaches operating temp). It's almost as though one of the components is reacting to the change, but I can't figure out which.

Thanks in advance for any clues.


-.b
 

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I believe the vacuum leak is at where the throttle body attaches to the intake if no gasket is present
I think after it warms up the expansion causes it to leak
 

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You might also want to clean your actual intake/butterfly area. even the smallest of carbon on the closing area will throw the idle off once it warms up. You won't notice when the engine is cold.
 

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1970-1995 Range Rover Classic
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42 Posts
Discussion Starter #4
Thanks all for the suggestions. I just use a very thin film of blue RTV for gasket material when putting the plenum and throttle body on the intake - I've never seen a gasket used in these positions on the Rover V8. I have a few spare assemblies so I can run one through the parts cleaner and switch out dirty parts for cleaner ones. The act of disassembly and re-sealing may be the trick.

-.b
 

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1995-2002 Range Rover Classic
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1,413 Posts
since you're lifting the plenum, re-torque the intake manifold bolts they tend to loosen and of course your idle suffers and you show false air.
another point of leaks is the intake boot, if it is the original it may have fissures which widen as under hood temp rises.

use some carb cleaner while running, spray around intake. if idle rises suspect that area. with new 02 sensors, on 14cux disconnect battery to reset adaptations.
 
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