Hick-ups?

[katana]

Hi all!
While cruising at constant speed of about 65, my 4.5 has hick-ups. As if there are misfirings. Happens also when I accelerate, but with no kickdown. Where to check first? Had the spark plugs out the other day and there was a bit of carbon(?-anyway it's black and you can scratch it off) residue on them. Car started up fine after that. Was a little rough before.
Thanks,
Fritz

[Tomguy]

If it's surging, it usually means you're lean; if it's stalling out, it's too rich. That's what I think they are, anyway. I might have it backwards. Black plugs normally indicate you're running rich. Start looking for vacuum leaks before you adjust the mixture. Do a search on 4.5 and vacuum, you'll get a ton of results I bet.

[katana]

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This is something I found and will need to check because I took the plug apart and may have wired it wrong. Which wire in this plug goes where? I think there is blue and brown.

Thanks,
Fritz

[Tomguy]

Doesn't matter which wire is where - it's merely a resistor, polarity doesn't matter. However, if it's loose and not connected, you WILL run rich.

[katana]

Okay thanks. Now what happens if the previous owner tuned the engine without the resistor working. Looking at how corroded it was, it hadn't been hooked up for years...
Thanks,
Fritz

[Tomguy]

You really can't tune the engine without that hooked up, it'll run unpredictably (too rich when hot, too lean when cold outside). See how it runs with it connected properly first. Cruise at 75 in second gear for a few miles, if it surges you're lean, if it sputters you're rich. It won't harm the engine, just burn a lot of gas.

[billrei]

A quote from http://members.rennlist.com/pbanders/DJetParts.htm I keep posting, concerning the air intake sensor:

Function: Senses intake air temperature and sends signal to the ECU to provide mixture compensation.
Normal Value(s): 300 ohms @ 68 deg. F, about 100 ohms @ 122 deg. F.
Failure Modes
Open: Makes the mixture somewhat richer. Check with an ohmmeter.
Shorted: Makes the mixture somewhat leaner. Check with an ohmmeter.
Notes: The output of this sensor is used by the ECU to adjust the mixture for the intake air temperature. This is a secondary adjustment and has a small effect on the mixture. The sensor corrects for the decrease in air density with increasing temperature by leaning out the mixture. Disconnecting this sensor has the effect of richening the mixture, a common mechanic's trick.

[mbshop]

this is also a common symptom of a bad/misadjusted throttle switch.
also a badly adjusted inj system.

george