3 Things to Check if You Have a Cold Start Rough Idle (2023)


Here are the parts I used in this video:
Delphi MAF Sensor: amzn.to/3X366kB
Map Sensor: amzn.to/3ZpZvSO
Intake Manifold Gasket: amzn.to/3k1R9jX
OBD2 Reader: amzn.to/3ZuCOwU
Throttle Body Cleaner(might be cheaper in the store): amzn.to/3GXnBgw
Fuel Line Remover: amzn.to/3ZwMLdk
Torque Wrench: amzn.to/3QwFdD6
Orange Grip Mats: amzn.to/3ZmBCvv

I have a Patreon and I would love your support: www.patreon.com/BuildsUnited
You'll have behind the scenes access and more!

Check me out on IG: instagram.com/buildsunited_

I have a website:


Due to factors beyond the control of Builds United, I cannot guarantee against improper use or unauthorized modifications of this information. Builds United assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. Use this information at your own risk. Builds United recommends safe practices when working on vehicles and or with tools seen or implied in this video. Due to factors beyond the control of Builds United, no information contained in this video shall create any expressed or implied warranty or guarantee of any particular result. Any injury, damage, or loss that may result from improper use of these tools, equipment, or from the information contained in this video is the sole responsibility of the user and not Builds United.

Furthermore, the links posted within the description may or may not contain affiliate links. If used, I trully appreciate the support!


Welcome back to another video.

The Tahoe has been having a rough cold star Idol today.

We are going to figure out what's going on with it.

So first I got a new map sensor.

So how was it old? And in with the new with the map sensor housing, we moved, you got to get a thin flat head.

And your goal is to pinch this tab within the little sliver in the MAF sensor housing.

And at the same time as you press down on that latch, you want to go ahead and grab some sort of pliers and pull the sensor out.

And it should come right out, although faulty map sensors are very common and causing a rough eyewalk.

Hold starts.

That was not my issue.


I spent a lot of money on that map sensor from Advanced Auto.

So the next common issue would be the map since it going bad.

Luckily, there's a cheap option off of Amazon, it's located, right on top of the manifold.

So since Stone Parts had it didn't fix the issue, let's, go ahead and figure out what the heck's going on to do that.

I grabbed my OBD2 reader, plugged into the OBD2 spot I'm just going to turn the key to accessory.

Because as soon as the engine warms up, I will not have the symptoms anymore.

I'm gonna take my phone out open up the car scanner app connect to the unit I want to check out the live data I'll be checking out the fuel trim levels.

So these numbers should be as close to zero as possible I'm, getting diagnostic because of having won a misfire.

And it is running lean so I'm, assuming it's a vacuum link.

So to test a vacuum link, we got some fluid I've seen people use brake, cleaner, fluid and I'm just going to use air intake cleaner.

So I am spraying where the intake manifold meets up to the block of the engine.

And watch these short-term fuel.

Trim level bank, one go down to zero as I spray it.

So I know, for sure that there's a leak on bank one on the driver's side of the intake manifold, so then I proceed to try out the left side or Bank two.

And we got the same results.

And just like that we have found out that there was an intake.

Manifold gasket, leak got the Tahoe in the garage just received the gasket.

And we got Layla, hey, what's up.

Remember that map sensor? Well, we are going to move that.

Oh, yeah, don't forget to unplug.

The battery the map sensor the vacuum line.

You have an eight millimeter.

Now we need a trim remover tool.

This will just come right off unplug.

The throttle sensor remove the power from the alternator.

Now, this plate, which just unscrews be sure to organize all your screws, because if not and you lose them that would suck get a quick puppy break tab on the back is pull up and you lift up.

Now we need to remove the fuel injectors, that's, four on both sides.

So you just pull up comes right out.

Remove the brake, booster clamp and its hose.

We now need to move this fuel line right back here, you can move it with these plastic pieces.

Or this metal tool is ours, seven zero.

Zero, two, four, this line will be pressurized.

So heel will come out.

So in order to release the pressure, we will come on the left side of the engine.

Take off this.

You want to get a flathead and just press that nipple down the drive is gonna be soaking with gas.

Do not give it to your dog instead, put it away to pull it in and press this tool in you just it'll just slide in, oh, there's still fuel on it.

Do you remember that scene and saw where the girl had to get the key and like this little metal box, and she like stuck a hand through the box and her hand got stuck.

This is basically the same mechanism, except you don't lose a hand if you aren't smart enough to move your hand.

And now we can push all this wiring behind the intake.

Now we have these bolts holding down to intake, they're, essentially all around grab eight millimeter and start removing them.

The ones in the back is kind of tight to get to so you will need a smaller wrench this two way back here on both sides.

So it's gonna be here, hey, squeeze once you break them loose do them by hand and there's one more way back there, that's, the tightest one on the left side to get to far back the plug right here lift at the back it'll, be pushed right out push that through see push down on this lock.

And you pull back that's, at least what the pros say, thank you.

And now it's time to wiggle out the intake, manifold can anybody tell why I had an intake manifold leak when I replace the motor I, just didn't, install it correctly, I know how to install it now and I'll show you, you can definitely tell I've been running lean for far too long.

That means I'm getting too much oxygen compared to how much gas I'm getting.

And you can really tell with the carbon buildup around the uh, the inlets of the heads, the intake Parts holes for the air for the heads head air, head air holes.

We can go ahead and take out all the bolts you just kind of throwing them sideways and come out so don't, lose them.

Just go ahead and clean these surfaces as well.

This is how you properly install an intake gasket.

It literally Clips in wow, isn't that magic.

Why did I not know that when I installed it? The first time this would be a good time to clean these throttle body, I'm gonna use my throttle body cleaner that I use to test the intake, manifold gasket leak.

And now with all that finished, we can sew that sucker back into the engine on the engine on the engine and I'm not going to show you the whole process just do everything in reverse.

And with the proper torque specs on the intake manifold, because if not you can mess things up, so also look up the right crisscross pattern that you'll need to do when you're installing the intake manifold.

Okay, I'll show you the crisscross pattern because I'm a nice person.

Well, I guess, I forgot how an LS should idle, because that definitely sounds a lot more healthy.

So that is hell.

You fix a Refinery I recommend checking the intake first with the test that we did look at those numbers, make sure they're around zero.

If they're way too high, you have an issue because I just simply did not install the intake, manifold gasket correctly, I mean, that's an easy mistake, isn't it.

Everything I use in this video will be linked down below for your convenience.

A rough idle, especially at cold, start can be pretty finicky to diagnose.

But those are three things that you can do to try to fix your rough idle.

Thank you to all my patrons for supporting me.

This is Chris Bill's night.

It always appreciate and respect.

Another I'll, see you in the next video in the next video we are going to detail the Mercedes is filthy and replace a few parts to finally register it.

So I can drive it on the road.


3 Things to Check if You Have a Cold Start Rough Idle? ›

What to Look For: A lousy temperature sensor results in rough idle during cold starts. Once warm, the problem may be less noticeable. Faulty Airflow Sensor – Like the temperature sensor, the airflow sensor helps your car know how much fuel to use, based on the amount of air in the engine.

What can cause rough idle on cold start? ›

What to Look For: A lousy temperature sensor results in rough idle during cold starts. Once warm, the problem may be less noticeable. Faulty Airflow Sensor – Like the temperature sensor, the airflow sensor helps your car know how much fuel to use, based on the amount of air in the engine.

What are signs of rough idle? ›

A rough idle may include any of the following:
  • Idling below or above its regular speed.
  • Inconsistent RPM.
  • Shaking or vibration through the car.
  • A skipping, slipping sound.

What are the main causes of rough idle? ›

5 Common Causes of Rough Idle
  • Clogged Fuel Filter. Over time, your car's fuel filter can become clogged and will need to be changed. ...
  • Dirty Fuel Injector. The fuel injector dispenses fuel and air into the cylinders. ...
  • Faulty Fuel Pump. ...
  • Bad Spark Plugs. ...
  • Vacuum Leak. ...
  • Look for a Reliable Mechanic.
Mar 24, 2021

Why is my car idling rough at startup? ›

Causes of a rough idle. Many different problems could result in a rough idle for your car or truck, including: dirty fuel injectors, clogged air filters, bad spark plugs, and a variety of exhaust system issues.

How do you test a cold start sensor? ›

Start the engine and, using the procedure described in section 20, listen to the cold start injector (located on the air intake chamber). You should hear a clicking noise, meaning the injector is functioning. If a clicking sound is heard, let the engine reach operating temperature and repeat the check.

What controls cold start idle? ›

When a cold engine is started, a component called the auxiliary fuel injector sprays additional fuel into the intake manifold. The extra fuel helps the engine start faster. But we also do not want the fuel-air mixture to be too rich. So, the throttle valve opens to raise the engine's idle speed.

Does rough idle mean misfire? ›

Rough idle

A rough or uneven idle can be an indicator of an engine that is misfiring. The air/fuel mixture is disrupted which can cause the engine to jump up and down.

Why is my car idling rough and shaking? ›

One of the main reasons why your vehicle could be vibrating at idle could be due to worn out spark plugs. When a vehicle's spark plug is faulty, it can interfere with the air-fuel ratio leading to improperly firing cylinders, resulting in a misfire while idling. Replacing your spark plugs will solve this problem.

Can lack of oil cause rough idle? ›

Oil changes keep your car engine running smoothly. Rough idling, slow acceleration, and engine noises mean you need to replace your car oil.

How do you reduce rough idle? ›

How to fix it? Cleaning or replacing the fuel filter and adding a fuel injector cleaning treatment to the fuel tank should take care of clogged fuel injectors. If the rough idle persists, it's time to take your car to an auto repair shop.

Can a dirty intake cause rough idle? ›

Engine misfires, rough idling and hard starts can all be traced to a clogged engine air filter. The dirty air filter restricts the air supply to the engine causing unburned fuel to form a soot residue that accumulates on the spark plug.

What sensors can cause rough idle? ›

Oxygen (O2) sensor

An oxygen sensor monitors and analyzes the amount of oxygen in a vehicle's exhaust system after combustion. A dirty, damaged or malfunctioning O2 sensor (or sensors) affects the air/fuel mixture, causing the engine to idle rough.

What are the signs of a bad cold start sensor? ›

Symptoms of a failing cold start valve include failure to start your car and poor fuel efficiency. If your engine is flooding when you try to start your car, then the cold start valve could be leaking.

What sensors control cold start? ›

A thermotime switch, or TTS, is a sensor used to control the cold start enrichment process in some older fuel injection systems.

How do you test a cold start solenoid? ›

To test that the solenoid is working, disconnect the wire connecting it to the starter solenoid and run 12 volts to the cold-start solenoid from another source. If you do not disconnect the starter wire, the starter will engage while the engine is running.

How do you fix the cold start problem? ›

The cold start problem may be overcome by introducing an element of collaboration amongst agents assisting various users. This way, novel situations may be handled by requesting other agents to share what they have already learnt from their respective users.

Why does my RPM go up and down on cold start? ›

It is normal for the engine rpm to go up to about 1200 to 1400 rpm when first started and then comes down gradually. This is for emissions during cold start and considered normal.

Why does the RPM go up and down at cold start? ›

In colder temperatures, fuel is more likely to get bogged down and thicken. Therefore, the vehicle overcompensates for this by producing a higher RPM initially to move gasoline more quickly.

How do you diagnose a misfire? ›

These are the signs of a misfiring engine that you need to look out for:
  1. The engine loses power.
  2. It is difficult to start the engine.
  3. Fuel consumption rises.
  4. Emissions increase.
  5. The engine makes popping sounds.
  6. The intake or exhaust manifold backfires.
  7. The engine jerks, vibrates or stalls.
Jul 9, 2019

Can an o2 sensor cause a misfire? ›

Yes. While the damage may seem small initially, the longer you drive with a bad oxygen sensor, the worse the damage will become. Eventually, you may experience rough idling, poor acceleration, engine misfires, an illuminated check engine light, and failed emission tests.

What are 5 possible causes of a shaking vehicle? ›

Why is My Car Shaking? Top 7 Causes You Can't Ignore
  • No. 1: There's a tire problem. ...
  • No. 2: The brakes need repair. ...
  • No. 3: Your plugs have lost their spark. ...
  • No. 4: Your suspension system needs some TLC. ...
  • No. 5: Worn or bent parts. ...
  • No. 6: Low transmission fluid. ...
  • No. 7: Worn motor mounts.
Sep 30, 2019

What causes RPM to fluctuate while idling? ›

Engine hunting and surging at idle is usually caused by a fuel delivery, air leak, or governor system problem. Cleaning/overhauling the carburettor, adjustment of the governor, and/or changing the air filer may be required.

Can a bad PCV valve cause rough idle? ›

A PCV valve that's stuck open will allow too much air to enter the intake manifold, leading to a leaner idling fuel-air mixture. Stuck closed leads to a build up of pressure in the crank case which creates a variety of oil leaks! And this in turn can lead to a range of issues, including a rough idle.

Why does my car idle rough but drive fine? ›

A rough idling engine can be caused by spark plugs or spark plug wires. Spark plugs use the electrical current received from ignition coils to ignite the air/fuel mixture within the combustion chamber. A plug that is damaged or installed incorrectly can result in fuel being burned at an inconsistent rate.

What are signs of low engine oil? ›

Here's a list of some of the most common symptoms of low engine oil.
  • Oil Pressure Warning Light. The easiest way to tell if your vehicle is running low on oil is your vehicle's warning light. ...
  • Burning Oil Smell. ...
  • Clunking Sound. ...
  • Less Efficient Performance. ...
  • Overheating Engine.

Can bad gas cause rough idling? ›

Low Quality Fuel

Another reason why your car may be experiencing rough idling could be due to the use of low-quality fuel. You should always check the grade of fuel recommended by your car's manufacturer. For example, your car won't idle smoothly if you use 87 octane when 93 is recommended.

Will fuel injector cleaner help rough idle? ›

It works to dissolve fuel residue and carbon deposits to restore lost power, reduce rough idle and hesitation, restore octane requirements, and improve overall drivability.

Will seafoam fix a rough idle? ›

SEA FOAM MOTOR TREATMENT is a fast, easy and low cost DIY fix for solving the most common causes of rough engine idle.

Why is my engine sputtering on cold start? ›

Ray: The driveability problem could be caused by something such as a bad coolant temperature sensor, a bad air-mass meter, or even partially plugged-up fuel injectors. Any of those things could cause sputtering when the engine is cold.

Why does my engine grind on cold start? ›

So, what is that grinding noise you hear when starting a car? Most likely, if it is true grinding that you hear, the problem is related to the starter. Causes include the starter not lining up correctly with the ring gear on the flywheel, missing or damaged gear teeth, or a faulty solenoid.

What are the symptoms of a bad cold start sensor? ›

Symptoms of a faulty cold start valve:

Engine stalling – After your engine starts, you may experience stalling while you drive. This will either occur at higher RPMs or when you take your foot off the pedal. Rough idle – Your engine may produce loud noises or even vibrations when you are idling.

Top Articles
Latest Posts
Article information

Author: Aracelis Kilback

Last Updated: 03/10/2023

Views: 5273

Rating: 4.3 / 5 (64 voted)

Reviews: 87% of readers found this page helpful

Author information

Name: Aracelis Kilback

Birthday: 1994-11-22

Address: Apt. 895 30151 Green Plain, Lake Mariela, RI 98141

Phone: +5992291857476

Job: Legal Officer

Hobby: LARPing, role-playing games, Slacklining, Reading, Inline skating, Brazilian jiu-jitsu, Dance

Introduction: My name is Aracelis Kilback, I am a nice, gentle, agreeable, joyous, attractive, combative, gifted person who loves writing and wants to share my knowledge and understanding with you.