How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Matt Your Own Question
Matt, Engineer
Category: Car
Satisfied Customers: 21726
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
Type Your Car Question Here...
Matt is online now
A new question is answered every 9 seconds

cold start..rough..cylinders..Engine runs ok above ca 1500-2000 rpm.

Resolved Question:

Re; L 3.1 Jetronic on Lancia Thema 16v.from 1992, engine code834 B2.000 On cold start engine idle is rough at ca 600 rpm , as if it is running on 3 cylinders. Engine runs OK above ca 1500-2000 rpm. When engine is warm idle is OK at 900 rpm but pick-up is hesitant. It depends on ambiant temperature also. With ambiant temperature over 38C engine runs perfect. Please suggest what can be the trouble. kind regards XXXXX
Submitted: 5 years ago.
Category: Car
Expert:  Reecekerley replied 5 years ago.

Reecekerley :

Hi, I’m a moderator for this topic and I wonder whether you’re still waiting for an answer. If you are, please let me know and I will do my best to find a Professional to assist you right away. If not, feel free to let me know and I will cancel this question for you. Thank you!

Reecekerley, ASE Certified Technician
Category: Car
Satisfied Customers: 148
Experience: 25 years experience in the transmission and drive train industry.
Reecekerley and other Car Specialists are ready to help you
Expert:  Matt replied 5 years ago.

This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.
if the engine condition is the same then chances are the meter or the connection to it is faulty

Air leaks are very temperature dependent as gaps can open or close up as things expand with heat, so the weather and engine temperature can effect them.

This leads them to be quite intermittent in the case of mild leaks

its also worth cleaning the airflow meter by removing it from the car and spraying the exposed sensor wires inside the tube with a brake or switch cleaner - ensure that the cleaner is one of the old fashioned, non Eco type that does not leave a residue

On no account touch the sensor wires with anything physical as they are extremely fragile
Customer: replied 5 years ago.
As I mentioned all piping and trunk have been replaced so air leaks are out of the question.

So I removed the connector to the airflow meter, not quit easy and put it back on, even more of a struggle, but.....
Hey presto, the engine is performing as normal. Must have some corrosionin the contacts.After all the car is 20 years old.

I will spray it with contact cleaner later. Thanks for putting me in right direction

Expert:  Matt replied 5 years ago.
No problem
Matt, Engineer
Category: Car
Satisfied Customers: 21726
Experience: Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
Matt and other Car Specialists are ready to help you

Related Car Questions