Throttle cable has some slack too.....why would it continue to surge and high idle?

 

Could a blown head gasket cause surging and high idling?

 

Leaks at the intake will cause high idle. A bad iac or controller. Many things really.

 

Thanks for the reply.

The only thing I haven't adjusted is the Throttle Position Sensor. I'll try that next or replace it.

 

Everything was fine until I changed the floor mats around 400K....it's been a struggle ever since

Have you considered putting the other floor mats back in?

Sorry, I just had to ask....

 

I did throw those out....my wife was proud of me for that......I usually save everything.

 

Ahhh, it's her fault eh?

 

Seriously though, if you disconnect the iac and start car what does it do

 

I never tried that. I replaced the original IAC after multiple cleanings while in place which didn't help. If I place my finger over the opening at the throttle body with the new one in place, I can modulate the idle down but that's just a physical block.

 

I talked to someone today and they suggested double checking my water pump. If it's not pushing coolant, the IAC won't respond....and might explain why passive heating (baking in the sun) is affecting idle to lower it.

 

wow 420k miles, thats quite an achievement, you drive quite alot everyday huh?
and do test what tercel gts said, tell us what happens when the iac is disconnected

 

Effective troubleshooting (least amount of time & money spent) requires determining whether a part is good or bad BEFORE you replace it. It does you no good to replace a working part, the problem will persist. And when you do not know for sure whether a part is good or bad, you have to test it. And that requires measurements and specs that yields numbers which then can be compared to numbers in the manual to determine whether that part is indeed good or bad. If you replace every single component in the engine-compartment and the engine itself, you'll most likely fix the issue without ever figuring out what the actual problem was. But you'll end up with a HUGE pile of perfectly good spare-parts you won't need for decades, if ever. You need to get a vacuum tester gauge, voltmeter and measure:

- vacuum in intake-manifold with warmed-up engine, use one of the nipples near the throttle-body. Pick one that opens to the rear of the butterfly it's inside the manifold

- vacuum at FPR, use rubber-T and connect to FPR-nipple to maintain proper FPR function

- vacuum at MAP-sensor, again use rubber-T

- MAP-sensor voltage at idle with cold-engine
- MAP-sensor voltage at idle with warmed-up engine
- MAP-sensor voltage at 25mph
- MAP-sensor voltage when it does the surging (also good idea to watch manifold-vacuum during this)

 

You're absolutely correct DannoXYZ. My mindset as a non-mechanical weekend mechanic was to replace parts. Testing performance was not something I considered, or I probably thought it was beyond my skill set. I see that I need to adapt and get smart about what's going on. Thanks for putting me on the right track. I appreciate everyone's time and effort into these problems. I'll test these as suggested and report back.

 

Limited data due to kid's games/practices and rain, but here we go.....

FPR: 20.0 in. Hg warm @ 1600 rpms
MAP: 20.5 in. Hg warm @ 1600 rpms
Manifold: 21.0 in Hg warm @ 1600 rpms

I could not get any voltage readings from the MAP. There is crud around each wire which is making it difficult and I'm not sure exactly which wire has the feed and which wire is reference. I'll try again tomorrow when I have more time (and sun).

 

Does this crud have a color?; corrosion around a contact could cause some problems; to find which pin on the connect is the feed (12v), just unplug it and using a multi-meter set to read 12 volts DC; turn ignition key to the "ON" position (do not start) and then touch the red probe to each of the connector pins. The one which shows around 12 volts is the power wire.

 

Awesome! Thanks.....

The crud doesn't have a color.....it's not corrosion, it's just grey looking dust that's packed in against the wires. The black plastic sheath has slid back, probably years ago.

 

The three wires going to MAP-sensor should be:

- 5.0v regulated reference voltage
- ground
- variable output voltage signal

Simple enough to test each one with key ON, engine not running to determine which one is which. I think the MAP signal is a light-green/red-stripe wire. Here's what it should be sending at various vacuum levels:

3.96v = 112kpa, -3.6 in.Hg, 1.74 psi
3.6v = 100 kpa, 0 in.Hg, 0 psi (atmospheric)
2.4v = 60 kpa, 12 in.Hg, -5.8 psi
1.2v = 20 kpa, 24 in.Hg, -11.6 psi

The trick to monitoring this is to see if vacuum and/or MAP-voltage changes right before you have the surging issue.

 

Thanks for this info. DannoXYZ!!!

Yes.....this was tricky, just to get the dials readable through the windshield without them sliding or falling down. A two man job for sure......reading dials and writing down their readings while driving is not conducive with a healthy lifestyle!

For the MAP sensor, the feed line for my car was actually the middle pink line. The green with red stripe wire was the 5 volt reference.

Data:

@ ATM MAP 3.55 v @ 0 in Hg
@cold start MAP 1.41 v @ 20 in Hg
@run temp MAP 1.35 v @ 21 in Hg
@25mph/gear MAP 1.57 v @ 18 in Hg
@25mph/neutral
& surging MAP 1.57-2.21 v @ 15-20 in Hg

Vacuum readings were taken at the manifold. The MAP voltage reading did dip below 1.57 v during the surging but it was too transient and hard to read....maybe 0.82 v at times then fly up to 3.6 or so, but it quickly returned to 1.57 v if I was in gear and accelerating slightly.

 

So what do these numbers indicate, if anything? That my MAP sensor is fine.

 

MAP signal looks OK when the car is stable. Although manifold pressure should be around 24-in.Hg at 1600rpm. Lower vacuum is sign of intake leaks sucking extra air, thus the too-high idle. This is partly mechanical and adjustments:

- TPS angle @ closed position correct?
- dash-pot & hose working properly? at idle dash-pot should not have contact with throttle
- idle-valve, disconnect electrical connector to remove its function, is idle back at correct speed?
- check all intake hoses and clamps.
- use propane torch (unlit) to spray around all intake joints and seams to detect source of leak.
- measure resistant of ECT and IAT sensors with cold and warmed up engine. Are the readings correct?

I think this is a combo multipart issue and the surging is just a byproduct and symptom of whatever's causing the high idle. Something is letting in extra air. Fix that and the stumbling should be resolved as well.

 

Bad o rings on injectors often cause vacuum leaks.

 

OK.....I did the leak test and found that at some points in the vacuum lines there was some leaking due to craking.....so I replaced lines where I could and tightened up my air intake line (replaced) which really was a mess from doing patchwork fixes since the rubber and plastic was essentially falling apart from "age", new air filter, etc.


Also in the weeks prior to this, I replaced the water pump, replaced timing belt, the 2 flat belts and reset my timing with E1 and TE1 jumped (or at least I think I did that right). The water pump replacement was a chore.


It idles now close to 800 rpms (at cold start) but now the problem is rough starting. Once up to running temp, she humms and idles around 900-1000. I can live with that (I guess). But I'm worried about the rough starting problem, which she's never had. Also on driving it, she lags in second gear now. Does that sound like a timing issue? Maybe I didn't get the timing right.


Thanks in advance,
Steve

 

1. Measure the ECT and IAT resistances. These tell the ECU that you have cold-start conditions and it'll inject extra fuel and raise idle.

2. If the ECU doesn't sense cold-start, it won't inject extra fuel and raise idle. Should be around 1100rpm on cold-start which you don't have. So something's wrong with cold-start. Either ECT/IAT sensors aren't correct, or idle-valve's not letting through extra air for fast-idle.

3. Re-measure intake-vacuum & new idle and MAP-sensor output. I think we're getting close.