My truck is simply running bad! It will start up fine, and idle fine in park, but when I put it in gear it idles really bad, slow like it can't breath it sounds like it's coughing lowly. When I give

Asked by Dec 17, 2014 at 06:11 PM about the 1985 Chevrolet C/K 10

Question type: Maintenance & Repair

It some gas it will rev up but just
won't move very fast, even if I let it
warm up for a good amount of time it
still won't go right, please help idk of
that's the right model but it's a chevy
long bed pickup 1985

17 Answers


Hate to say it, but you need to inspect all the ignition parts for causes of multiple misfire or cross fire. The plugs first of course, then work through wire inspections and ohm checks. In the cap, you may find carbon tracking, and wear, aftermarket anomalies in the parts. The advance weights under the rotor for excess wear at their pivot studs and holes. If you have a 12v test light you can cancel cylinders by probing the cap boots. before disassembly. Then having an A/c delco module solves a bunch of variables etc. You must look for what is amiss on yours. If you suspect vacuum leaks you can use spray carb clean to find them. A bad advance diaphragm can mess up your runability. an improper assembled cap/ coil/ ground strap relationship may lie under the cover on top. Carb issues with fuel delivery would suggest fuel pressure and volume tests were in order. An ineffective accellerator pump can be fixed by just lifting the top off and replacing at the bench. If you see black shilt in the float bowl you could have a saturated vapor cannister. Do some inspecting including Timing and advance readings before disassembly or jus go to your favorite tune-em-up shop and plead ignorance, but want a well explained estimate.

2 of 2 people found this helpful.

Coughing lowly, i am not sure what that means but it makes me want to verify it with a tech experiencing the issue as you point it out. If it jumped at the timing chain or had cam going round on you, there are some easy tests before really getting into it. So, how many miles since it really had some educated wrenches under the hood ?

1 of 1 people found this helpful.

Quite a few I only have about 118,000 on it


I think you should check the vacuum modulator. Once you put the transmission in gear it activates the vacuum modulator and if there's a leak, it's not going to shift or run particularly well.

5 of 5 people found this helpful.

How does the turbohydramatic activate the modulator when it's in gear? The vacuum supplied is constant and it is whatever the engine has available. If the throttle opens it loses any vacuum signal. His 85's concern is he seems to idle enough to stay running, but cannot rev up in park or accellerate at all when in gear. If you were saying it is stuck in a higher gear ? That would mean the governor was not returning as the vehicle slows and that pulls on the other end of the valve the modulator pulls on. This means to me that you are saying the trans is trying to start from a standstill in third lets say. Right? Because a stuck modulator would cause it to be in a lower gear and it would accellerate well up to the shift point. A bad running engine would have a weaker vacuum signal and not have the modulator in play to delay an upshift. He could eliminate that possibility or verify it using First with the gear range. pull it into low range, however, That does not free a stuck governor. His trans downshift or upshift history was not discussed in his description.


So his modulator vacuum signal at the hose would be the same as manifold vacuum read at the base plate of the carb. If it was low or not existing to read , it would mean he had a break in the tube or hoses supplying vacuum from the rear of his intake manifold. If his modulator was mechanically stuck or physically bent or damaged, that would be visible upon inspection. There are times the trans specialist sends the vehicle to the tune-up line because the poor run of the engine and weak vacuum makes it seem like the trans is at fault.


NOW, a partially blocked exhaust or bent exhaust, or plugged cat can produce weak and dropping vacuum signal that gets worse as it warms up. He needs to be sure his choke is not stuck shut from a bad choke pull off and a plugged crossover. There are smells and you notice excess heat in the engine compartment sometimes. You really need to tow it to a tech to get a general idea of what to describe it as. Look at your maintenance records and see if you are neglecting the maintenance like filters or have some of the things going on that I have listed. Return with readings and inspections done. Get a vacuum gauge on there, and read a tuneup manual that teaches vacuum gauge readings and what they mean. Free at the library, chiltons is decent, when they are the Bible sized ones.


You could run your carb idle circuit adjusters in and count, then back them out to base line setting and see , watching the gauge. But we will see if you can define the problem a little better.

1 of 1 people found this helpful.

I just received an email about this offering other info that pertains to an 85 truck. The spark advance issues capt p kelley was talking about from the knock sensor related parts makes me think the description of "coughing lowly" could mean detonation. if your advance somehow was being turned up or down by those parts ? or stuck somehow? it would be like spring and weight sticking in a mechanical advance perhaps. he was stating the advancer parts can be updated by using the better distributors before, i think, they had vacuum advance. As always, it seems the age of the emission system can cause operation that pollutes and hurts. He was describing his first experience with idle circuit adjustment gaining another 50% to his fuel mileage. Wayta go !


Please update and say if you improved your issues. what did you replace, delete or improve or adjust? we were having trouble really perceiving the description till capt. p kelly offered the electronic advance malfunction as a thought. I have not seen it in this thread but the link took me here. Hopin you haven't given up !


I am having the same issue. I pulled my engine sbc 350. Had it completely rebuild. Had my 1406 carburetor rebuild. Install a HEI distributor and my truck idles great but when I get on the street it runs bad. Changed back to the original HEI distributor the with the plug on the side and my truck still runs really bad but idles great. Can someone help.

2 of 2 people found this helpful.

it could be a vacuum leak


Well it turns out I didn't have vacuum to the Lock up switch that's by the brake booster mounted on the fire wall. Thanks for your help. Now Im having problems getting it started. I crank on my engine then it almost feels like my engine is going to lock up. I had my battery tested and they said it was good , so as soon as I get a chance im look at replacing the starter. This project is turning into a head scratcher. lol


I have a 1973 k5 blazer and has the same issues starts and runs great in park but when in gear it acts like it's starving for air. It backfires through the exhaust and carb, doesn't want to shift on its own, and it doesn't go over 40 mph. Would this be a vacuum leak or bad vacuum modulator?

3 of 3 people found this helpful.

I have a 1981 Chevy full size blazer sometimes when I'm driving it starts to eagle real bad like if the truck is fall apart seems to be coming from the front end some whr if any one has in put thanks


I have a 85 chev 4x4 350 when it running it idles fine but when I put it in drive it wants to die out but it was running fine


how do tell if the torque converter is bad

1 of 1 people found this helpful.

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