1990 YJ Howell TBI high idle - JeepForum.com
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Unread 03-30-2015, 10:05 PM   #1
oxtail4
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1990 YJ Howell TBI high idle

Got done with the Howell TBI retrofit onto my 1990 YJ with 258 cid. All is well, good starting, driving all smooth. Idle, however is high, about 1500 rpm.
Looked for vacuum leaks - haven't found any
Tested idle air controller per Howell - jumpered A/B terminals and unplugged, idle still high.
Drilled out idle screw and adjusted per Howell manual - lowered idle down to about 1100 rpm - ran out of adjustment.
Any other ideas out there?

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Unread 03-30-2015, 10:55 PM   #2
mike134
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how long did you run it for? when the engine is cold, 1100 is about normal. It should drop as it warms up to temperature.
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Unread 03-31-2015, 08:57 AM   #3
oxtail4
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Starts at 1500, lowers to 1100 at normal operating temps.
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Unread 03-31-2015, 09:13 AM   #4
jbolty
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Do you have access to an OBD1 scanner?

I had that issue and it's been a few years but I seem to recall it being the MAP sensor.

Call Howell, they are very helpful. The normal tech guy will start firing questions at you so before you call note everything. Timing, what you've done and tested and any other possible adjustments.
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Unread 03-31-2015, 10:18 AM   #5
oxtail4
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No OBD1 scanner. Is there one you can recommend - I get a lot of hits if I google.

I've talked to Howell. They asked told me to check the IAC - tested OK. I'll try them again and see what they say.
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Unread 03-31-2015, 01:19 PM   #6
jbolty
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you need a scanner that will read GM vehicles. The computer will report to the scanner as a late 80s small chevy pickup
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Unread 03-31-2015, 01:23 PM   #7
boduke5051
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Does the Howell come with the GM OBD1 type diagnostic connector? If so, I would think you could read the codes by the check engine light by jumpering the A and B terminals. Or has the Howell system done something different that would cause this to be a bad idea?

Link below:

http://www.obd-codes.com/faq/read-gm...codes-free.php
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Unread 03-31-2015, 02:03 PM   #8
oxtail4
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If the computer was throwing a code, the check engine light should come on (I thought). When I bypass the computer, I do get the single blink as it is supposed to per Howell.
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Unread 03-31-2015, 02:27 PM   #9
jbolty
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if you have a scanner you can read the sensor voltages and get some sense of what's happening that may not be causing a code.
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Unread 03-31-2015, 03:42 PM   #10
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I see where you're going now. I didn't think of that because all of the scanners I ever had weren't nice enough to show actual live data like that.
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Unread 03-31-2015, 05:51 PM   #11
oxtail4
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I'll be on amazon tonight to order one.
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