Rough idle after changing spark plugs

[Eddy_444]

Hello,

I have little Suzuki Swift 1.5 GLX '08 that just hit 50k. Great little thing. I thought I'd change the spark plugs since I didn't know the last time they were replaced. After changing them out for brand new genuine NGK iridiums, when starting the car: the rev meter dips to around 350 RPM and the car shudders, it then gradually gets back to a normal range of around 600 - 800 RPM where the car is idling smoothly. Same issue when stopping: the car judders and then gradually corrects itself. This never happened before changing the spark plugs.

Not sure what the issue is. I'm sure they're not the spark plugs as they're brand new, and look fine. The ignition leads are in good condition, too, given the car's age.

Any advice would be appreciated.

[paintman]

Refit the old plugs & see if the problem remains or clears.

I don't know what's involved changing the plugs on these but if you've had to remove/disconnect things are you sure they're all back in place & secure?

Edited by paintman on Wednesday 9th February 11:01

[steveo3002]

swap the old ones back maybe a dud plug...are all the new ones same or one wet ?

may also have damaged a lead when pulling it off

[GreenV8S]

Are they the same part number or at least a similar spec?

Have you gapped the new plugs?

Some plug leads are not easy to fit and it can be easy to leave the plug lead attached by the shround but not making good electrical contact. It's even possible to pull the connector off the conductor when disconnecting the lead if you pull it by the lead.

It sounds as if the problem is intermittent so unlikely you've got plug leads cross connected but it's another possible failure mode.

[trickywoo]

The main feed to the plugs has a stupid design. I pulled the wire out of mine by pulling the boot with my hand and not gripping the end with pliers. Could you have done the same?

I had to buy a new lead.

[Chris32345]

GreenV8S said:

Are they the same part number or at least a similar spec?

Have you gapped the new plugs?

Some plug leads are not easy to fit and it can be easy to leave the plug lead attached by the shround but not making good electrical contact. It's even possible to pull the connector off the conductor when disconnecting the lead if you pull it by the lead.

It sounds as if the problem is intermittent so unlikely you've got plug leads cross connected but it's another possible failure mode.

You shouldn't gap iridium type plugs

[Tyre Smoke]

Where did you buy the plugs from? Plenty of fake NGK on the bay.

[paintman]

Chris32345 said:

GreenV8S said:

Are they the same part number or at least a similar spec?

Have you gapped the new plugs?

Some plug leads are not easy to fit and it can be easy to leave the plug lead attached by the shround but not making good electrical contact. It's even possible to pull the connector off the conductor when disconnecting the lead if you pull it by the lead.

It sounds as if the problem is intermittent so unlikely you've got plug leads cross connected but it's another possible failure mode.

You shouldn't gap iridium type plugs

But you should check that they have a gap.

Watched an apprentice mechanic competition on one of the TV channels some years ago which included changing a set of plugs.
The plugs were brand new in their individual boxes.
Unknown to the competitors one plug in each set of 4 had had its gap closed completely - as might be the case with one that had been dropped.
One competitor didn't bother looking at the plugs but just fitted them.
Then spent the rest of the time allowed trying to find why the car was only running on three cylinders.
Never occurred to him to remove & check the plugs as part of the investigation.

[Eddy_444]

Thank you all for your replies. I'll refit the old ones tomorrow and that'll at least tell me if its a plug issue. As for the new ones, they're definitely genuine and the correct type of plugs. Purchased from eBay albeit from a repuatable seller in Opie Oils. All wires are where they are meant to be and securely in place. Further, they come pre-gapped and from comparing the new and old side by side, they all have the same gap.

trickywoo said:

The main feed to the plugs has a stupid design. I pulled the wire out of mine by pulling the boot with my hand and not gripping the end with pliers. Could you have done the same?

I had to buy a new lead.

This is what I'm thinking the issue is. However, I can't see anything that is wrong with the wires themselves. Was it visually apparent that you had pulled the wire from the cords?

Edited by Eddy_444 on Wednesday 9th February 19:24

[trickywoo]

Eddy_444 said:

Was it visually apparent that you had pulled the wire from the cords?

Yes. Came straight out with pretty much no resistance. I assumed I could pull it like a standard coil pack / plug head. How I laughed on a bank holiday weekend trying to get a new part.

[Jack2199]

Make sure the coil is pushed in properly on the plug. I don't know that design. But sometimes they can look n feel like they are on properly but it might not be.
Do you have a check engine light ? If you do, n u have a any scanner may help point you in a direction of a pertiqualr cylinder. If at all its not installed properly or a new plug is bad.

Very unlikely u have 4 bad plugs. As the others said swaping back to the old plugs could verify.

[AW10]

If the car eventually idles smoothly I doubt it’s the plugs - they don’t fix themselves. Far more likely to be an inadvertently disconnected vacuum line or electrical connector.

Based on your symptoms and ignoring the spark plug change I would have suggested a sticking idle control valve.