Idle Issues when Hot

pj31704 · Apr 12, 2014

I've been experiencing some issues with my idle speed while my engine is hot. It runs fine when cold start, idles great. However once I have been running engine for about 20+ minutes, the idle speed drops to about 600-700rpm's and sounds like the engine is struggling to stay running.

If I drive anywhere and shut the engine off, then try to start while engine is hot it will usually fire up but once I shift into Drive or Reverse the engine starts choking and will eventually stall. I'm not sure why it is only happening when engine has been running for awhile, any suggestions on where to start? I was thinking possibly electric choke is going bad? or vacuum leak somewhere? Just not sure.

Thanks for any help

pj31704 · Apr 12, 2014

Here are some pictures of the carb, not sure if there is anything that sticks out which may be causing an issue. I'm wondering if there is an issue with the electric choke or the vacuum lines in the front of the carb(whether it should be hooked up to the left or right plug). The last picture is of the intake manifold, there is an opening and I'm not sure if this is needing to be plugged or just missing a bolt??

Bully Bob · Apr 13, 2014

Some thoughts;

Did you set the two mixture screws when the eng, is completely warm..? If not.., do so.

Set (2 front screws) to the best idle & smooth.., then adj. the idle speed with the idle adj. *****.

(sometimes requires going back & forth a few times)

Idle speed should be approx. 7-8 hundred with automatic.

Goofy fuels these days sometimes req. moving the timing to get smooth idle.

Is the modulator on the trannie in good shape..?

That bolt hole is simply an attach hole..., usually for a vac. manifold.

The right/left vac. ports on the lower carb. are one in the same.

fyreduck1921 · May 31, 2014

I had a similar problem on my 76 Bronco. I have an Edelbrock intak and 4 barrel carb. According to my local shop, the electric choke on the factory 2 barrel carb ran on 5 volts, wired off of the stator on the alternator. The Edelbrock requires a full 12-volts. They ran a new power wire directly from the fuse box and now my hot idle is much better. Not sure if this helps. Good luck.

pj31704 · Jun 18, 2014

Thanks for the help,

I have finally had a chance to work on the rig, I have found the transmission modulator, however not sure to tell if it is malfunctioning?? Is there something specific I can try? Or should I just replace, most likely it is pretty old.

As for the carb, I have a 4 barrel and the electric choke is currently wired to the ignition switch. Which shows is 12V. Is this a correct hook-up? Or should it be wired differently?

Thanks for any help

Bully Bob · Jun 18, 2014

...."Is there something specific I can try?"

There shouldn't be any vac. leaks in the line. There shouldn't be any fluid in the module.

To my knowledge they req. 12v so, you should be ok.

pj31704 · Jun 18, 2014

I pulled the vacuum line to check and it basically crumbled into pieces. I'm sure that is not a good sign, it was definitely dried out. I looked but did not see any transmission fluid leaking. I got a new hose, but am having trouble finding the new modulator. Think the modulator may still be good?

Seabronc · Jun 19, 2014

If there was no trany fluid in the old hose, then the modulator is most likely good. If it had trany fluid, the modulator needs to be replaced.

>-

pj31704 · Jun 29, 2014

After replacing the old vacuum line and cleaning up the modulator I've taken the truck out twice, I haven't had any stall's after the engine was hot yet. I'm going to keep an eye on it for a few more times though, I just don't know that this was the main issue.

Is there any other issues which could be causing this problem that I can check? Or would the bad vacuum line really have been causing this?

Bully Bob · Jun 30, 2014

Good thinking.., these agravating issues don't always happen 1 at a time meaning sometimes 2 or three

will occur at the same time.

However, there isn't much under these hoods...! You have fuel, air, & elect. going on & that's about it.

It would help us help you if you continued on with your signature (under 33's) with all work, tune, parts

replacement, etc. The signature is fluid & you can update it any time you want.

Point being we can't remember what all everybody has already done to ea. vehicle.

EXAMPLE: what's the latest with the coil, module, dizzy, fuel pump..?

Idle Issues when Hot

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