SPONSORED LINKS

4cyl Fiero Stumbles when cold. Why?

Tiny
JAKSCARS
  • MEMBER
  • 1985 PONTIAC FIERO
  • 110,000 MILES
1985 Pontiac Fiero 2.5l 4 cyl. SE
When first starting, sometimes it idles fine. But when put under load the tach bounces all over the place and it runs rough. The whole car jerks.
Will continue to stumble for about 3-4 miles. Then its like nothing happened.
What is very odd - is no check engine light comes on and there are no codes stored in ECM.

I Replaced:
Distributor cap & rotor
Spark plugs & wires
Vacuum hoses
Battery
I checked the damper door under the vacuum motor to see if the Air Cleaner Temp Sensor was moving the door to regulate hot/cold air. And it is.
Mechanic suggested I look for leaks around intake manifold. But how do I get under by that to do that. Try to spray ether from underneath the car?

I really don't want to continue buying parts to guess at fixing it. The Air Cleaner Temp Sensor is $50 or more where I live.

Anyone else have any other ideas?
Much appreciated, thanks in advance.
SPONSORED LINKS
Friday, July 13th, 2012 AT 4:27 PM

7 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Egr valves are common failures for this condition. You should check it for proper operation. Take off the vacuum line and see if the issue is gone.

85 is way too soon for codes for these issue.

Otherwise, could need injector cleaning, coolant sensor or tps.

Roy
SPONSORED LINKS
Was this
answer
helpful?
Yes
No
Friday, July 13th, 2012 AT 4:29 PM
Tiny
JAKSCARS
  • MEMBER
  • 5 POSTS
Took off the vacuum line at EGR. Problem remains.
Is there anything I can do to test tps or coolant sensor?

Thanks for the reply
Was this
answer
helpful?
Yes
No
Friday, July 13th, 2012 AT 6:08 PM
Tiny
JAKSCARS
  • MEMBER
  • 5 POSTS
Another note. I'm noticing the idle is staying up around 1500 it used to be at around 1000. Maybe IAC valve is bad?
Was this
answer
helpful?
Yes
No
Friday, July 13th, 2012 AT 6:11 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
A scan tool can monitor the sensors. You need a shop with a scan tool for this portion.

Roy
Was this
answer
helpful?
Yes
No
Friday, July 13th, 2012 AT 6:12 PM
Tiny
JAKSCARS
  • MEMBER
  • 5 POSTS
I replaced IAC valve and so far it seems ok/better no stumbling at all. True test is tomorrow morning I guess
SPONSORED LINKS
Was this
answer
helpful?
Yes
No
Saturday, July 14th, 2012 AT 4:32 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good luck
Was this
answer
helpful?
Yes
No
Saturday, July 14th, 2012 AT 6:25 PM
Tiny
JAKSCARS
  • MEMBER
  • 5 POSTS
I ended up replacing the coolant sensor and ignition module too. Something has definitely changed. Now its' like when I hit a bump (maybe coincidence) and the engine is cold. Sometimes it will stumble when I first start it and idling, other times only when I put it under load. But the stumbling doesn't last as long and things seem to have somewhat improved. What the hell?
Was this
answer
helpful?
Yes
No
Sunday, July 15th, 2012 AT 3:55 AM

Please login or register to post a reply.

Related Engine Hesitate Content

Vacuum Leak Test and Repair
VIDEO
Vacuum Leak Test and Repair
Instructional repair video
Hesitation
GUIDE
Hesitation
An engine hesitation is an interruption of continuous power during acceleration. When a engine is hesitating it will cause the car to lunge or surge which will cause a...
VIEW MORE

Sponsored links