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Discussion Starter · #1 ·
Hello folks, This is a first! I own a 98 Dodge Ram 1500 Quad cab; 308 engine, with about 97,000 miles. About 5000 miles ago my truck started idling fast, immediately after startup. This is not a constant idle speed, but where it revs up an additional 500 rpm above normal idle speed. This increase in RPM occurs over and over, sometimes 5 times in a row, sometimes 15 times in a row, once I had to shut off the engine. But in each case when the engine warmed up, the problem quit. I had thought the problem was fixed, by having my dealer install a new gasket in the engine. The problem ceased until this morning, our first cool, high humidity morning. As a matter of fact, this never happens in the afternoon, only at first start up of the day!

My dodge dealer in Oklahoma City is a moron, I have had it in the shop 4 times and the problem is still not fixed. I've had a tune up, water de-carb of the engine, gasket replaced and a intensive check of the wiring. I think the wiring harness could have some kind of short, is this possible? What would make my truck idle normally for 2 seconds, then jump 500 rpm, drop off and repeat the senerio over and over?

This is the strangest issue with a truck I ever ran across, someone must have an intelligent answer for me!
 

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Lets start simply. You don't mention checking for any codes that may have registered. Others can correct me if I'm incorrect but I think you can still get the codes on the '98 by cycling the key (turn the key to "On" position then "Off" 4 times. On the fourth cycle On, leave it on and count the blinks of the Check Engine Light. There will be a pause between each set of blinks). Let us know what the codes are if any. The best bet for capturing a code would be after one of these episodes with the idle running high.
 

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4x4, Straight pipe roar!
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The idle on my truck seems out of wack sometimes too. It will go up to about 2k rpm and stay then if I rev it it will come down to normal. I think its the TPS but I haven't changed it yet. TPS could be your problem as well.
 

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The Green Machine
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Could be the Idle Air Controller also - take it off and clean it, or just replace it.
 

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******* SPACESTATION
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Could be the Idle Air Controller also - take it off and clean it, or just replace it.
:stu:

to isolate that it is the IAC, unplug it and see if your idle steadies out. It may not be at the correct speed, but if it doesn't jump around then you can probably get away with cleaning it...or just replace it.
 

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Discussion Starter · #6 ·
I appeciate the ideas! I'm printing the suggestions and taking them to my NEW dealers service department tommorrow, So with the bills I have describing what has been done, and your suggestions maybe we can get the problem narrowed down. I'll let you know what the service department says.
 

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my response likely wont be of any help, but hey... gotta put my penny in.

the Beast does this on rather nipply mornings, the idle at normal operating temps is about 5-600 rpms, but on those rather nipply mornings itll sit at 1465 for a few seconds then drop to about 1000, and after a little putting itll idle normally. i know nothing about mechanics, but my only thought is that, with as many miles as your engine has, even though its FI, i might need a quick warm-up in the morning. if it still idles high after the first startup, then i have no advice, just listen to the guys who know what theyre talking about.
 

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IAC would be my guess. Do our engines have an Igntion control module or is that all part of the ECU?
 

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******* SPACESTATION
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Do our engines have an Igntion control module or is that all part of the ECU?
timing and fuel are handled by the PCM.

also, this is not such a 'strange problem'.

i know nothing about mechanics, but my only thought is that, with as many miles as your engine has, even though its FI, i might need a quick warm-up in the morning. if it still idles high after the first startup, then i have no advice, just listen to the guys who know what theyre talking about.
all engines, fuel injected or not, need to reach operating temp before they run optimally. In carbureted cases, this is done with a choke, which limits the air coming in and thus increases the fuel to air ratio to a richer condition.
With multi port and throttle body, there is no choke but the injectors put more fuel to the motor until it gets to the proper operating temp or the 02 sensors are warm enough to provide the PCM with the fuel ratio.
 

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My vote is a bad or dirty IAC also. Remove the tb and the sensors and clean well with spray carb cleaner. Clean the plunger on the IAC with a rag with cleaner on it. Put it back together and try it. If it still does it, it's probably a bad IAC. Mine did that - and I fixed it with a good cleaning....
 

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Racinfan83 said:
My vote is a bad or dirty IAC also. Remove the tb and the sensors and clean well with spray carb cleaner. Clean the plunger on the IAC with a rag with cleaner on it. Put it back together and try it. If it still does it, it's probably a bad IAC. Mine did that - and I fixed it with a good cleaning....
That's what I did with a TPS problem, which was identical to the symptoms described above.
 
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